I don't know, the term "Role Playing Game" is such a complex, controversial, and convoluted term it has little to no substantive meaning, so why the hell not?

Some people say that the statistical basis for the characters is the glue that holds the genre together, so while Zelda, on its face, seems no less an RPG than, say, Demon's Souls, it still doesn't meet this criteria.

I think Zelda is the game responsible for the junction of puzzles, combat, and exploration that define the majority of today's action/adventure games. So let's go with that. Adventure.