I'm curious about these things too! for AI to generate art it needs to "train"(steal...) on other people's works, but this art style is unique, that's why I'm really doubtful.. there are ai tools to just polish the actual drawings of course, and also now that I'm thinking about it the artist could generate the body and then draw face, hair etc... a hybrid art is also an option I guess?
(this all is just a speculation on my part. I'm not a fan of baseless accusations, and I'm not actually accusing anyone!!)

I just can't help the feeling ://