As far as I can tell, Ehrman is right about that point. The earliest versions we have of the books of the Bible are very different from the versions we all read today.
At least 19 of the 27 books in the New Testament are forgeries.
Forgeries is a very strong word, stronger than I would choose. But the evidence is clear that these books have been significantly and substantially altered. Sometimes it was a transcription error; often it was insertion or deletion to fit a particular audience or a particular agenda.
So he thinks he proves the Gospel According to John is a so-called forgery? Or does the earlier apply to the manuscripts, not to the followers? Pick up the blue copyediting phone, please.