Yes, and I've read them before and didn't see anything about non-scholarly authors needing permission from authors to write a companion text or encyclopedia. Fair use is something different than writing about a text. There are no restrictions on that, and there should not be. I certainly haven't seen what this encyclopedia is doing (nor do I care, in point of fact), but if it's accurately called an encyclopedia then it is simply an informational source that will not contain extensive direct quotations from the Harry Potter books. The fact is that it may be a terrible book that adds little original thought, but in that case a lawsuit isn't necessary - the book will sink on its own merits.