Leanpub books are self-published, and authors choose their own categories. If you think a book is under the wrong category, the best thing to do is to let the author know about it.

Leanpub authors typically like being informed about things like this - here are the instructions for contacting them:

http://help.leanpub.com/en/articles/3852119-how-can-i-contact-a-leanpub-author