Ehrman's Misquoting Jesus - Chapter 2 "The Copyists of the Early Christian Writings"

In Bart Ehrman's Misquoting Jesus, the second chapter deals primarily with the issues of 1) Who was copying the text and 2) Editorial practices of those scribes.

Ehrman makes a statement in the chapter:

Because the early Christian texts were not being copied by professional scribes, at least in the first two or three centuries of the church, but simply by educated members of the Christian congregations who could do the job and were willing to do so, we can expect that in the earliest copies, especially, mistakes were commonly made in transcription.

This seems to be contrary to what Philip Comfort says in his book Encountering the Manuscripts. Comfort believes there was a scriptorium in both Alexandria and Oxyrhynchus that were in full swing by the second century AD. If this is true, does this make Ehrman's claims of inept scribes obsolete? Are there good reasons to believe that there wasn't a scriptorium in Oxyrhynchus by the mid-2nd century AD?