Could it not also be that people who happen to have less grey matter in those "self-control" areas, will (statistically) tend to be prone to drink more alcohol?

Could it not also be that people who happen to have less grey matter in those "self-control" areas, will (statistically) tend to be prone to drink more alcohol? That is, the causality could run the other way. It takes some self-control and restraint to moderate one's consumption, after all.