The average house is not at all more expensive in China than in the US.
It is true that in particular cities like Beijing or Shanghai the average sits around $7-9k per square meter (divide by 10 roughly for square foot), far higher than the average in the US. (divide by ten roughly for square foot). That's way more than in the US. But then consider these are megacities with a GDP of roughly half a trillion dollars. About half a million millionaires live in Beijing, Shanghai and Hong Kong. These are the top tier cities of the 22nd century's superpower, prices are going to reflect the notion that property in these cities should keep its value and appreciate strongly.
Median wages are already on par in these cities with various eastern-european countries. And income inequality is among the worst in the world, so you've got this small percentage of people who can elevate property prices to ridiculous heights. Only Shanghai and Beijing each have a population equivalent to 25 times San Fransisco, so a few rich people adds up to ridiculous prices.
I'm not saying these prices necessarily make sense, I certainly wouldn't buy there. But it's also not impossible to see why they're this high.