First, there were thousands of them. Someone having thousands of books is not unreasonable, of course, but both the breadth and depth of this collection is such that it is extremely unlikely it is someone's personal library.
Sounds like my personal library actually.
Second, the PDFs aren't the actual books. They are just short blurbs describing the book and containing download deep links into bookfreenow.com. A couple examples [1] [2]. Clicking to create an account so you can start downloading redirects through some ad companies (and possibly some shady affiliate marketing companies), eventually reaching some download site (I think) that tells you no free slots are available and asks you to make an account.
Well that’s a lot harder to explain in charitable terms! So is this even piracy, or just some kind of scam based on the promise of piracy?