I've seen something similar with my fitness. I've gone from competitive powerlifter to very obese to moderately fit, and the ways in which it changes the way almost everyone interacts with you, all the time, is just insane - from the quite subtle (being more deferential, more pleasant, slightly more generous with their time) to not subtle at all ("you're so smart! You look so shy; I wouldn't have guessed you're so smart until you started speaking.")
I feel like that's pretty likely a bigger element of it when I was younger, though I'm sure it always figures in to some degree. Although part of it is circular: when people all treat you like you're nicer/smarter/etc. you feel more confident, too.
But some of it was just a bit too much of a stretch to just be confidence. I'm /generally/ a pretty confident person, and comfortable with people, and the difference in how many people suddenly can vs. can't find the time of day for you is pretty dramatic.
And, of course, some of it was just not subtle at all. I'd been told pretty frankly I was too fat to be a doctor. Because, you know, clearly my personal struggles with my weight have a direct correlation to my ability to diagnose your ailment. (Okay, I'm still salty about that one.)
