Hmmm... you may be on to something there. I certainly can't disprove your theory based on the samples. It's not completely out of spec for what human illustrators sometimes do, but there are some things that seem a bit... odd.

https://m.media-amazon.com/images/I/710rEGCuE-L.jpg - the hand in the center of the image seems a bit off, like it was replaced later.

https://m.media-amazon.com/images/I/71vW6lumrpL.jpg - text in the book is suspiciously like what some of the AIs generate, although I don't recall that I've ever seen it projected onto an object quite like that; people who have more experience with it than me care to pipe up?

On the other hand, I can't say it's obviously AI either. It's hard to tell when someone who knows what they're doing may also be doing exactly the same analysis I'm doing here, and cleaning up the tells. If you pick up any illustrated book and stare at it hard enough for AI tells, you'll probably find some.