Honestly I've noticed a lot of it is confidence and mannerism. My partner has a friend who's over 6ft and 250lb who got stabbed and mugged within a month of living in our city. I'm a little under six foot, 120lb, and I'm an acute psych nurse specializing in the management of high violence risk patients, and I'm friends with at least a few of the homeless dudes (they make great drinking buddies, they know all the best area gossip).
While most of what I do is just not taking stupid chances, a significant portion over it is just "swagger" and being willing to take charge of a situation and get something done when it needs to be. I suspect it was a compliment because you were asking at the time why you're not as well-liked or approachable as you'd like to be. I often have difficulty making friends because of how much living in that mindset for as long as I have has affected my hypothetical "aura." People know I'm a protector / healer type, but definitely not in a hugger kind of way!
I don't like being in charge either, but when shit is actively hitting the fan, I'm often the only one willing to do it, and every time I've refused shit just hits the fan even harder so now I just deal with it.