The front page of the book directly links to https://github.com/0xAX/linux-insides/blob/master/CONTRIBUTI..., which makes it abundantly clear that this is the author of the book.

> They clearly made an effort to stay anonymous.

The word you're looking for is "pseudonymous", which is a very, very, very different thing.

Again, why do you care?

I don't understand your question. Obviously the source is a critical factor in evaluating information, which I'm sure you know, so what do you mean?