Peter is in my opinion making the mistake of comparing the united states arable land map to other countries. The US is a vertiable juggernaut when it comes to agircultural stuff. Other countries are able to play and feed themselves but it takes time. Also its location location location.
As you can see from the arable land map the western half of so of China is pretty much shit when it comes to growing stuff. Now look at the darkgreen where stuff is grown dollars to donuts if you slap a population map over it the areas where china has the most people would be where most of the food is grown.
In agergate yes most of china has shitty land for growing food and thats why the population lives where its grown. Most of russia's food is grown in that agercultural triangle with the vast majorty being legit shit for growing food.
That said China's problem is the imputs to feed their massive and aging population, which is going to be an increasingly hard challange as globalization breaks down.