It's been ages I've been to law school, but I believe the commercial distribution of copyrighted material, including electronic (P2P) file-sharing or the dissemination of download links is unlawful. Borrowing copyrighted material falls under fair use. I am quite sure that Bart neither had any criminal intent nor acted with a view to gain, so let's not assume the worst, but rather wait for someone's review of the afore-mentioned audio book.
Yes, I believe so. In practice (not law), "fair use" in the US (like "fair dealing" elsewhere) seems to have come to mean "republishing small bits of things wherever it's convenient and not too dickish to do so". (The actual right seems narrower and more complex, though IANAL.) I don't think that any similar assumed (let alone actual) right exists in Japan; though yes, schools are in some ways anomalous.Fair Use is more about using sections of a copyrighted work (reporting, treatsie, research, discussion, etc).