Eh?
The "fragment" Stanton speaks of above is the Muratorian Fragment. I do not know how the above is supposed to bolster the possibility that Celsus had read Irenaeus or vice versa.
A while back I had segregated the words of Celsus and Origen's summarizations of other points Celsus had made, and concluded that whoever this Celsus was, he was not a highly regarded Greek philosopher (known or unknown) but more likely an opinionated tutor of philosophy.
In fact, Origen only responded to Celsus' criticisms because Celsus had pushed his special "hot button" by the following:
4:23 In the next place, … the race of Jews and Christians, he compares them all "to a flight of bats or to a swarm of ants issuing out of their nest, or to frogs holding council in a marsh, or to worms crawling together in the comer of a dunghill, and quarrelling with one another as to which of them were the greater sinners, and asserting that God shows and announces to us all things beforehand; and that, abandoning the whole world, and the regions of heaven, and this great earth, he becomes a citizen among us alone, and to us alone makes his intimations, and does not cease sending and inquiring, in what way we may be associated with him forever."
And in his … representation, he compares us to " worms which assert that there is a God, and that immediately after him, we who are made by him are altogether like unto God, and that all things have been made subject to us, -- earth, and water, and air, and stars, -- and that all things exist for our sake, and are ordained to be subject to us."
And, according to his representation, the worms -- that is, we ourselves -- say that "now, since certain amongst us commit sin, God will come or will send his Son to consume the wicked with fire, that the rest of us may have eternal life with him."
And to all this he subjoins the remark, that "such wranglings would be more endurable amongst worms and frogs than betwixt Jews and Christians."
Origen assumes that this Celsus was a well known Epicurian philosopher by that name, then picks apart any statement of his that does not conform to what he thinks an Epicurean should say. In real life we call this setting up straw men, from which we learn way more about the man who sets up such straw men than about any real-life versions of the straw men which the author chosen to abuse.
As a result, we can tell almost nothing about what Epicurians said about Christians, etc, from Against Celsus.
I'll see if I can put a copy online (say by tomorrow).
DCH