The difference is NPCs exist only for the main character's experience. Oblivion's Adoring Fan does not have a life outside of interacting with the main character or an existence outside of when the human in the external reality controls the main character in the simulated reality. In our reality there is apparently no main character. Everything and everyone simply is. To learn one is an NPC is to realise that everything one has done is artificial and confined to the boundaries of someone else's experience. A created slave with a hollow origin and no means of escaping a forced purpose.