It appears to me that there are actually two different general stances that Celsus' True Discourse takes, which are slightly confused by Origen in the first two books (but not by much). The first one is the one above, which is the position of the "Jew," which is that Jesus was a deceiver but, still, just a man.
The second one emerges in the third book of the Contra Celsum, where Origen starts interacting with the statements made by Celsus directly.
Earlier Origen points out that Celsus takes some sort of 'docetism' to be the doctrine of the Christians.
http://www.newadvent.org/fathers/04161.htm
There is also a quote from book 4, chapter 19.Chapter 69
After this, Celsus, confusing together the Christian doctrine and the opinions of some heretical sect, and bringing them forward as charges that were applicable to all who believe in the divine word, says: Such a body as yours could not have belonged to God. Now, in answer to this, we have to say that Jesus, on entering into the world, assumed, as one born of a woman, a human body, and one which was capable of suffering a natural death. For which reason, in addition to others, we say that He was also a great wrestler; having, on account of His human body, been tempted in all respects like other men, but no longer as men, with sin as a consequence, but being altogether without sin. For it is distinctly clear to us that He did no sin, neither was guile found in His mouth; and as one who knew no sin, God delivered Him up as pure for all who had sinned. Then Celsus says: The body of god would not have been so generated as you, O Jesus, were. He saw, besides, that if, as it is written, it had been born, His body somehow might be even more divine than that of the multitude, and in a certain sense a body of god. But he disbelieves the accounts of His conception by the Holy Ghost, and believes that He was begotten by one Panthera, who corrupted the Virgin, because a god's body would not have been so generated as you were. But we have spoken of these matters at greater length in the preceding pages.
Chapter 70
He asserts, moreover, that the body of a god is not nourished with such food (as was that of Jesus), since he is able to prove from the Gospel narratives both that He partook of food, and food of a particular kind. Well, be it so. Let him assert that He ate the passover with His disciples, when He not only used the words, With desire have I desired to eat this passover with you, but also actually partook of the same. And let him say also, that He experienced the sensation of thirst beside the well of Jacob, and drank of the water of the well. In what respect do these facts militate against what we have said respecting the nature of His body? Moreover, it appears indubitable that after His resurrection He ate a piece of fish; for, according to our view, He assumed a (true) body, as one born of a woman. But, objects Celsus, the body of a god does not make use of such a voice as that of Jesus, nor employ such a method of persuasion as he. These are, indeed, trifling and altogether contemptible objections. For our reply to him will be, that he who is believed among the Greeks to be a god, viz., the Pythian and Didymean Apollo, makes use of such a voice for his Pythian priestess at Delphi, and for his prophetess at Miletus; and yet neither the Pythian nor Didymean is charged by the Greeks with not being a god, nor any other Grecian deity whose worship is established in one place. And it was far better, surely, that a god should employ a voice which, on account of its being uttered with power, should produce an indescribable sort of persuasion in the minds of the hearers.
Yet Celsus seems to go further than quoting the arguments of the "Jew" and further than pointing out contradictions between the Gospels and the belief that Jesus had the body of a god. Celsus seems to argue, moreover, in the passage below, that the supposed appearance of the body of a god (which, when seen, is but a "shadow") could be nothing more than "inventions," "fictions," and "myths."Others, then, may concede to Celsus that God does not undergo a change, but leads the spectators to imagine that He does; whereas we who are persuaded that the advent of Jesus among men was no mere appearance, but a real manifestation, are not affected by this charge of Celsus.
Here we find Celsus taking up the opinion of the "docetics," essentially, according to which Jesus was a "shadow" or a "phantom." And it seems that Celsus can press this so far as to say that the disciples had only imagined their Jesus, who was but a "shadow" ... and thus created fictions and myths out of something that they thought they had seen. And Celsus compares it to the similar case of Asclepius, who many claim to see and who claim that the spirit of Asclepius has healed him, although Celsus doesn't seem to grant Asclepius any real existence.
If you read between the lines, that seems a substantial shift from the position of the "Jew" (and one not commented on frequently).
http://www.newadvent.org/fathers/04163.htm
Origen also frequently alleges that Celsus is an atheist and an Epicurean, who thus has no real belief in Æsculapius; which would suggest, if true, that the analogy drawn by Celsus between Æsculapius and Jesus draws attention to some doubt on the part of Celsus regarding the latter god's "existence."But this low jester Celsus, omitting no species of mockery and ridicule which can be employed against us, mentions in his treatise the Dioscuri, and Hercules, and Æsculapius, and Dionysus, who are believed by the Greeks to have become gods after being men, and says that we cannot bear to call such beings gods, because they were at first men, and yet they manifested many noble qualifies, which were displayed for the benefit of mankind, while we assert that Jesus was seen after His death by His own followers; and he brings against us an additional charge, as if we said that He was seen indeed, but was only a shadow!
... And if they who would defend such beings betake themselves to allegorical interpretations, we must examine each individual instance, and ascertain whether it is well founded, and also in each particular case, whether those beings can have a real existence, and are deserving of respect and worship who were torn by the Titans, and cast down from their heavenly throne. Whereas our Jesus, who appeared to the members of His own troop — for I will take the word that Celsus employs— did really appear, and Celsus makes a false accusation against the Gospel in saying that what appeared was a shadow. And let the statements of their histories and that of Jesus be carefully compared together. Will Celsus have the former to be true, but the latter, although recorded by eye-witnesses who showed by their acts that they clearly understood the nature of what they had seen, and who manifested their state of mind by what they cheerfully underwent for the sake of His Gospel, to be inventions? Now, who is there that, desiring to act always in conformity with right reason, would yield his assent at random to what is related of the one, but would rush to the history of Jesus, and without examination refuse to believe what is recorded of Him?
And again, when it is said of Æsculapius that a great multitude both of Greeks and Barbarians acknowledge that they have frequently seen, and still see, no mere phantom, but Æsculapius himself, healing and doing good, and foretelling the future; Celsus requires us to believe this, and finds no fault with the believers in Jesus, when we express our belief in such stories, but when we give our assent to the disciples, and eye-witnesses of the miracles of Jesus, who clearly manifest the honesty of their convictions (because we see their guilelessness, as far as it is possible to see the conscience revealed in writing), we are called by him a set of silly individuals, although he cannot demonstrate that an incalculable number, as he asserts, of Greeks and Barbarians acknowledge the existence of Æsculapius; while we, if we deem this a matter of importance, can clearly show a countless multitude of Greeks and Barbarians who acknowledge the existence of Jesus. And some give evidence of their having received through this faith a marvellous power by the cures which they perform, revoking no other name over those who need their help than that of the God of all things, and of Jesus, along with a mention of His history. For by these means we too have seen many persons freed from grievous calamities, and from distractions of mind, and madness, and countless other ills, which could be cured neither by men nor devils.
Now, in order to grant that there did exist a healing spirit named Æsculapius, who used to cure the bodies of men, I would say to those who are astonished at such an occurrence, or at the prophetic knowledge of Apollo, that since the cure of bodies is a thing indifferent, and a matter within the reach not merely of the good, but also of the bad; and as the foreknowledge of the future is also a thing indifferent— for the possessor of foreknowledge does not necessarily manifest the possession of virtue— you must show that they who practise healing or who forefell the future are in no respect wicked, but exhibit a perfect pattern of virtue, and are not far from being regarded as gods. But they will not be able to show that they are virtuous who practise the art of healing, or who are gifted with foreknowledge, seeing many who are not fit to live are related to have been healed; and these, too, persons whom, as leading improper lives, no wise physician would wish to heal. And in the responses of the Pythian oracle also you may find some injunctions which are not in accordance with reason, two of which we will adduce on the present occasion; viz., when it gave commandment that Cleomedes — the boxer, I suppose— should be honoured with divine honours, seeing some great importance or other attaching to his pugilistic skill, but did not confer either upon Pythagoras or upon Socrates the honours which it awarded to pugilism; and also when it called Archilochus the servant of the Muses— a man who employed his poetic powers upon topics of the most wicked and licentious nature, and whose public character was dissolute and impure— and entitled him pious, in respect of his being the servant of the Muses, who are deemed to be goddesses! Now I am inclined to think that no one would assert that he was a pious man who was not adorned with all moderation and virtue, or that a decorous man would utter such expressions as are contained in the unseemly iambics of Archilochus. And if nothing that is divine in itself is shown to belong either to the healing skill of Æsculapius or the prophetic power of Apollo, how could any one, even were I to grant that the facts are as alleged, reasonably worship them as pure divinities?— and especially when the prophetic spirit of Apollo, pure from any body of earth, secretly enters through the private parts the person of her who is called the priestess, as she is seated at the mouth of the Pythian cave! Whereas regarding Jesus and His power we have no such notion; for the body which was born of the Virgin was composed of human material, and capable of receiving human wounds and death.
... Now, in answer to this account of Aristeas, we have to say, that if Celsus had adduced it as history, without signifying his own assent to its truth, it is in a different way that we should have met his argument. But since he asserts that he disappeared through the intervention of the divinity, and showed himself again in an unmistakeable manner, and visited many parts of the world, and made marvellous announcements; and, moreover, that there was an oracle of Apollo, enjoining the Metapontines to treat Aristeas as a god, he gives the accounts relating to him as upon his own authority, and with his full assent. And (this being the case), we ask, How is it possible that, while supposing the marvels related by the disciples of Jesus regarding their Master to be wholly fictitious, and finding fault with those who believe them, you, O Celsus, do not regard these stories of yours to be either products of jugglery or inventions? And how, while charging others with an irrational belief in the marvels recorded of Jesus, can you show yourself justified in giving credence to such statement as the above, without producing some proof or evidence of the alleged occurrences having taken place? Or do Herodotus and Pindar appear to you to speak the truth, while they who have made it their concern to die for the doctrine of Jesus, and who have left to their successors writings so remarkable on the truths which they believed, entered for the sake of fictions (as you consider them), and myths, and juggleries, upon a struggle which entails a life of danger and a death of violence?
... And because it was impossible that the reasons of such things could be discovered by men with perfect exactness, it was deemed safe that no mortal should entrust himself to any being as to God, with the exception of Jesus Christ, who is, as it were, the Ruler over all things, and who both beheld these weighty secrets, and made them known to a few.
The belief, then, in Antinous, or any other such person, whether among the Egyptians or the Greeks, is, so to speak, unfortunate; while the belief in Jesus would seem to be either a fortunate one, or the result of thorough investigation, having the appearance of the former to the multitude, and of the latter to exceedingly few. ...
(There does seem to be some wriggle room here... as there often is. Someone might say that it is only the post-mortem "existence" of Aesclepius or Jesus that is ever challenged. But it seemed worth mentioning. And such a claim runs against the sense that Celsus didn't, it would seem, regard "Jesus" to be a man in the first place--that's the opinion of his "Jew"--but rather as the alleged appearance of 'the body of a god', which he heard from Christians. That retort also contradicts the nature of the "appearance" of Antinous, who is also compared to Jesus, with the former "appearing" to a "multitude," and with the latter "appearing" only to "exceedingly few" that were "members of his own troop" [something mentioned also at the start of this passsage]. So it is not clear that the discussion by Celsus is limited to the 'resurrection' appearances and post-mortem existence.)