Do Overweight people gain muscle in legs faster than Skinny people?

I'm 14, 250 pounds. I am a linemen for my school football team. I am doing conditioning now(which is torture :|), and I have noticed my calve muscles are a LOT bigger than those of a guy that is in shape and can run more than me. My guess is because I have more weight to carry than they do. Is my guess correcto?