It seems that several of the WikiProjects that are currently being worked on are aimed at improving stub articles ("an article deemed too short to provide encyclopedic coverage of a subject"). From the screenshot of the article the author references, his article was a stub. My guess is that someone tried to improve it, thinking that a book's coverage would be deemed encyclopedic, then when it was deleted, the person who deleted saw that it had previously been a stub and didn't look further into it.