right, this comes close to rejecting the frame, which I think you could fairly do.

viewing npc as a category of person is inherently an ego driven, narcissistic way of looking at things. It is a viewpoint that lacks a theory of mind.

This essay implicitly supposes that the npc has a mind + motivations and that those motivations are more important to the npc than the player character. I'd extend it to say that if you are an npc you are a player character; you're just in a different game. Village Blacksmith Simulator, where you make horshoes, fend off pickpockets and sometimes a hero's dragon fight flattens your shop and you start over.

The flaw is assuming the player character is always the same.

Ironically the people who view others as NPC (and say so in a disparaging way) are likely more one dimensional themselves. I think you're spot on with the narcissism viewpoint.