Okay, first time forum poster here, having not read any of the FAQ or rules I'll try to be as concise and polite as possible.
As a amateur designer of and having played pen and paper RPG's for over a decade I have to say that yes, your friend is correct in that GTA and Assassin's Creed ARE in-fact RPG's. They are Sandbox RPG's based in a fairly close to reality setting and shining examples of such. RPG is short for Role Playing Game, and as such any game where you play the role of a character be it human, alien, robot, or even an animal or diety and interact with the world around that character is an RPG. The lines blur because an RPG game could be based around a modern FPS platform, an over-the-top turn based strategy platform, or even a game where you play a god ordering one's minions about. There are lesser and greater degrees of these variables of course - the case of Black and White being an RPG is pretty flimsy after all - but the definition of Role-Playing a character is all that's needed.
As a amateur designer of and having played pen and paper RPG's for over a decade I have to say that yes, your friend is correct in that GTA and Assassin's Creed ARE in-fact RPG's. They are Sandbox RPG's based in a fairly close to reality setting and shining examples of such. RPG is short for Role Playing Game, and as such any game where you play the role of a character be it human, alien, robot, or even an animal or diety and interact with the world around that character is an RPG. The lines blur because an RPG game could be based around a modern FPS platform, an over-the-top turn based strategy platform, or even a game where you play a god ordering one's minions about. There are lesser and greater degrees of these variables of course - the case of Black and White being an RPG is pretty flimsy after all - but the definition of Role-Playing a character is all that's needed.