Sweat and tights=sexy?

So normally I somewhat understand men, but I simply cannot grasp the concept of checking girls at the gym. I walk in and I see some skinny thing in a leopard patterned top and bare stomach, and I guess showing off her abs can be sexy, if you're into that kind of thing. I also understand why guys might check out the female Zumba instructors who wobble their asses like most of us have to be pretty damn shitfaced to even dare attempt. But why, why and why do guys check me out at the gym?
So I'll admit, I've been working out and I'm proud to say I lost 2 kg in the past 3 weeks. My shoulders are also looking quite toned, and my legs are more or less strong. But me in washed out H&M tights, a random loosely hanging top that I tied together with a hair tie around my hips because otherwise it goes down to my knees, my face red and my collarbones glancing with sweat.. and heads turn!
Last night, the Zumba instructor asked me to stay after class and dance with him! I mean, what!?

I brought it up over dinner with my mother and she, sticking with her theory that men are too intimidated by me to give me a try, suggested that I'm less "out of reach" when I dress down. But I mean, come on, I'm not that hot. Maybe average, but not like men look at me and think they'll never have a chance, that I'm like way out of their league. Or do I come off as super arrogant maybe, even though I try not to nowadays?

Could someone please give an opinion?

x
/E