Before anyone goes on a wild goose chase, this excerpt is on the opening of Chapter 4 instead of 5 in the first edition.
Anyone surprised to find that public domain art is determined to be AI generated does not realize that feeding an LLM requires a lot of art, and public domain is the easiest one to come across. AI detectors, as far as I know, check AI signs, and (most) AI signs came from their use by public domain artworks.