I just double checked and this one has "erotic novel" labeled on the cover, above the title, so at least they're being clear about it. ;) FWIW, erotic novels are often labeled as erotica, or as the other-genre they're enhabiting, or just as fiction (like James Lear's "The Back Passage"). There's a ton of explicit sex (happens to be gay) in an "Agatha Christie style whodunit" (from back cover copy) but it's labeled Fiction/Gay & Lesbian. The fact that Cleis publishes it clues you in.

In a way, a lot of these labels are a bit arbitrary, and depend on the publisher/how they think they can market it, but the term romance is a particularly sticky one, particularly when it's given to a book that isn't.