this is so unlikely, that one of his authors corrected it, announcing that Jesus did not baptise, but his disciples did (Jn 4.2 seeking to correct Jn 3.22; 4.1). We should not believe this. The synoptic gospels have no trace of Jesus or his disciples baptizing, and they had no reason to omit it, … The whole passage (Jn 3.22-4.3) is a quite overblown attempt ... inspired ... At the same time, it contains the correct view that some of Jesus’ ministry took place ‘when John had not yet been thrown into prison’ (Jn 3.24), …
John 3.22-4.3 RSV
After this Jesus and his disciples went into the land of Judea; there he remained with them and baptized.
 John also was baptizing at Ae'non near Salim, because there was much water there; and people came and were baptized.
 For John had not yet been put in prison.
Now a discussion arose between John's disciples and a Jew over purifying.
 And they came to John, and said to him, "Rabbi, he who was with you beyond the Jordan, to whom you bore witness, here he is, baptizing, and all are going to him."
 John answered, "No one can receive anything except what is given him from heaven.
 You yourselves bear me witness, that I said, I am not the Christ, but I have been sent before him.
 He who has the bride is the bridegroom; the friend of the bridegroom, who stands and hears him, rejoices greatly at the bridegroom's voice; therefore this joy of mine is now full.
 He must increase, but I must decrease."
 He who comes from above is above all; he who is of the earth belongs to the earth, and of the earth he speaks; he who comes from heaven is above all.
 He bears witness to what he has seen and heard, yet no one receives his testimony;
 he who receives his testimony sets his seal to this, that God is true.
 For he whom God has sent utters the words of God, for it is not by measure that he gives the Spirit;
 the Father loves the Son, and has given all things into his hand.
 He who believes in the Son has eternal life; he who does not obey the Son shall not see life, but the wrath of God rests upon him.
Now when the Lord knew that the Pharisees had heard that Jesus was making and baptizing more disciples than John
 (although Jesus himself did not baptize, but only his disciples),
 he left Judea and departed again to Galilee.
I expect most people can agree that Jn 4:2 is a later addition, but is it not possible to see Jn 3:22-23 as historical and Jn 3:24 as a later addition?
It seems that Casey is just picking the bits he likes rather than treating the whole section in the same way.