So, it's not surprising the average Chinese person has a decent understanding of how a basic democracy works.
In some ways, China is also not THAT much different, either. But it is more different than pretty much every other major economy in the world.
I mean, for one, it does not even put on a charade of being a democracy. It pretends to be communist (economically), but in a lot of ways it is more capitalist than a lot of the West. And the scale of the government is enormous. It's much more different, and there's really not much of a reason for many people in the US to have a decent idea of how it works.
China's government does not affect our daily lives that much - at least not yet. And Americans (like most people) are mostly concerned with themselves.