Hmm, interesting topic. If it's a complete alternate universe story (same character names, but some significant change, be it history, locale, motivations, or what have you), then it should be advertised and acknowledged as a fan fiction. However, if the characters have been renamed and other details altered, then it could be listed as an original fiction. Look at 50 Shades of Grey. It was a fan fiction but, with new character names and other changes, became - poof! - original fiction.

Without knowing the specifics, I don't know how similar the novel and the show are. There's always the possibility that he/she honestly wrote it without realizing the similarities. I have heard many cases here on dA with artwork and original characters where one deviant accuses another of stealing their work, and the other has never seen or heard of the first person, much less their work. It's hard to say. Of course, this would not be the case if the author blatantly uses the original characters' names, same locales, scenarios, etc..