There is a big push right now (Common Core) for kids to get used to reading "informational text". This means reading every day stuff like news articles, instruction manuals, financial summaries, utitlity bills....
Is that what your teacher is talking about? I would choose a kid's magazine in a subject he enjoys (sports Illustrated for kids, national geographic for kids, and whatnot).
If she specifically wants him to read non-fiction books (or a different type of fiction than what he currently likes), you will have to go back to the source and ask her because we don't know what she wants.
Generally at that age ANY reading is better than no reading, so if she has a specific goal in mind for him you should find out what it is.