I agree that it is ambiguous given that Adobe provides both ADEPT and PDF. Even written more properly as "Adobe, Encrypted (DRM)" many people would be mislead. I would probably make a mistake in interpreting it the first time around (if I wasn't forewarned by this thread), but I wouldn't blame the bookseller. It would be my fault for not clairifying the matter. I don't think that they are being deliberately misleading.

Sorry, but I cannot agree. That would be like saying a truck is not a vehicle because a truck won't fit into a parkade. The term ebook (like vehicle) is generic. While some ebooks should be reflowable so that it works well on portable ereaders like your Boox 60 and Sony 950, some ebooks are not easy to format in that manner. Yes, LotR should have been one of those reflowable ebooks. On the other hand, I read a lot of ebooks that are PDF because they are much more demanding than the typical novel (e.g. technical books).