Can I call wow an FPS because I can scroll all the way into my hunters POV?
Trying to define games strictly based on the word for word acronyms is pedantic. You could literally make a case for every game to have multiple types, hell you could call MW3 games RPGs if you really wanted to because you can level and change out your gear and you play a role.
MMORPGs generally have similar traits that are self evident, for example a persistant world where all the player are a part of. D3 doesn't have this.