I think one can argue it is an rpg, though it doesn't have all the trappings of a traditional rpg game (IE character stats/attributes, gain exp, etc).
However from the perspective of an actual rpg where your can take any of the characters and then choose how you want them to act out their roles, what choices they make, all of t hat in turn (to me) is why it can be considered an rpg.
I mean lets take a step back and look at where rpgs came from, D&D, one of the main points of rpgs like D&D and others is just that, that you create a character and then you choose what you want them to do. The main difference here being that it's not set up against you choosing your characters "Stats" and things like that.
On the flip side one could argue it's more of an rpg then some other "rpg" games are that are more linear in nature and don't allow you to really make choices when it comes to the story and things like that (Horizon, Monster Hunter World, God of War, etc).