That's true in a way, but it's not quite that simple. Hormones play a huge role in the affair. You can eat less to be less weight, but your body chemistry will largely determine if that weight is muscle or fat.
Those with higher levels of testosterone will naturally have a much leaner physique given the same caloric intake and activity level. Those who have tried steroids will tell you that once you stop, you'll get fat. That's because testosterone dictates how much muscle your body can hold, and once you lower it the body will no longer want to hold that much muscle, and your body will turn all those extra calories you're eating into fat instead of muscle.
Anybody can be lean if they're 130 lbs, but try being lean when you're 170, 190, 200, 220 lbs. There's an upper limit to how much muscle you can naturally build. It's also why women can't get as big as men- naturally, of course. Once you stick that needle you can manually decide what your T level is going to be, even if you're a woman.
Take Jay Cutler for instance- he's 5'9", and during bulk up phase he's over 300 lbs of solid muscle, only 7% bodyfat. Competition weight he's 260+ lbs of only 2% body fat. Obviously this is not natural. When you shoot T, you can hold as much muscle as you want (but it's not good for your health)
