What is insane about this is that this is not aggregate wealth, it's per capita. So you can't even argue that it's because China's population is over four times larger. And a lot of this is because of debt. Americans are crazy indebted.
Some of the stuff you see happening in China is just unthinkable by western standards. Working class families can actually afford to save up enough money to buy their young adult children their own home. Imagine that!