[Ographer]

It sounds like you may be comparing the population density of a large, diluted area and not the downtown areas alone.

It doesn't get much denser than downtown Chinese cities, they have specialized in high-density mega-sized apartment buildings.

Even large US downtowns are dwarfed by the average Chinese city downtown flush with LED skyscrapers. They have way more people and manufacturing than other countries so it shouldn't be too surprising.