I knew that Schezwan tends to be spicier than the Cantonese but didn't know
that rice is not the main carb of China.

Rice does not grow above a certain latitude. It is said that south of
Shanghai, rice is the staple, where as wheat is staple for north of
Shanghai, and that city has a mix of both. Since the northern portion
of China is larger in area than the southern, it could be argued that
more Chinese eat wheat as a staple compared to those who eat rice.