I’m not familiar with this book, but just from looking at the Amazon link it seems likely to me that those comments from the author were meant to be funny and were not a genuine expression of anger. The book also appears to be intended as humor, so it may be an effective promotion after all.
This must be related to the Real Ultimate Power webiste, which contains wisdom such as “Ninjas are mammals” and instructions on how to turn a long-sleeved black tshirt into a totally sweet ninja mask.
Yeah, I’d say the response is meant tongue-in-cheek.