Well yeah that's basically Solipsism, the belief that one is the only entity in a universe created of their own thoughts. Every input, be it a tree, a person, or a videogame character redesign with blue arms are really a manifestation of the observer (Chris).
Like the Monarch of Pointland from "Flatland".
I'll offer a counterargument that it's not that bad. I think Chris definitely recognizes that other people exist as independent entities. People with his condition don't assume that other people are NPCs, they just merely assume their actions are guided by the same thought processes and information as themselves.
Part of the failure of theory of mind is also expressed in the failure of object permanence, something that is usually developed before theory of mind. Chris has only the most basic level of object permanence -- once he has seen something he can understand that it still there when it leaves his view. What he lacks is the ability to anticipate things that he has not encountered yet. Things outside his immediate world are not real places to him (meanwhile, his imaginary world *IS* real, or at least more real than places, things, and people he doesn't know about).
To some degree this is a normal human trait. Ask someone to draw a map of their state and they'll normally exaggerate the size of the parts they are familiar with. Ask them to draw a world map and the same thing happens. The younger the person, the more pronounced the effect. With very small children they can only draw a map of places they have personally experienced.
To Chris, Central Virginia is basically the whole universe. He can hear about other places but they pale in comparison to the size and scope of Charlottesville and Richmond. When there are fires in Australia, ALL OF AUSTRALIA IS BURNING and thus PandaHalo dies because Australia occupies a smaller place in Chris's world than Ruckersville. Places like Baltimore and Philadelphia that Chris has been to are appendages hanging off the side of Virginia. There's a long straight line to Ohio vaguely in the back of Chris' mind, probably significantly shorter than in real life because he was probably lost in thought for most of the drive.
So while Chris can see information that there are billions of videos on youtube, his own internalized understanding is that there are only the videos he encounters. Thus, everyone sees the same videos he does, so when he posts a video EVERYONE will see it unless they're just not paying attention to youtube like he is.
So it's not that Chris doesn't think other people are real. He just only understands them as real in the context of his own experience. If they're outside of that experience, they just don't register, and any thoughts, feelings and behaviors that rely on experience that Chris does not experience himself are forever inscrutable to him, and can only be explained by assigning misunderstanding or malice to other people.
Again, this is a normal human trait that many people have trouble overcoming. Try getting a Christian to get along with a Muslim, or a Democrat to get along with a Republican. Most people can figure it out through actual interaction with others, but Chris can't even figure out why someone like Megan might not want to be touched because obviously it FEELS GOOD.
Chris doesn't think you're an NPC. He just only understands (and fails to understand) you through his own lens.
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