You already kinda said it—this is a problem with the relationship with your boss, not with the book.
With my boss, I can just say, "Honestly, this one was a miss for me. I appreciate the recommendation, and I wanted to give it a chance, but I didn't find much actionable substance in it. What did you get out of it?"
If you don't feel like you can do that, have a conversation with him about how he likes to receive feedback. If the answer is "he doesn't," it might be time to go boss shopping. But I doubt that will be the case.
So what does he want to be called? Just a rat? But - there are actual rats, which are already called rats. Unless those don't exist in this universe, "ratman" seems like a pretty reasonable term. He has both rat and humanoid features.