Sure, maybe I'd agree that they are people with masks are more likely to have good health habits, but I'd probably also assume that people with masks have worse

Sure, maybe I'd agree that they are people with masks are more likely to have good health habits, but I'd probably also assume that people with masks have worse health (even if they may have better habits). I think their health is more relevant than habits in this case. I would guess that people who know they get sicker than most will be more cautious than average, they've been dealing with it their whole life. Maybe not totally independently of how their health habits are taught to them, but I bet a lot of it is just experience. People know their bodies pretty well, even if they don't try very hard.