morningstar
Cathlete
Muscle does not weigh more than fat. 10lbs of muscle weighs the same as 10lbs of fat. Muscle just takes up less space than fat. So a 150lb person with lean muscle looks thinner than a 150lb person with less muscle.
It is like 10lbs of feathers compared to 10lbs of lead. You will have more feathers than lead but they will both weigh 10lbs.
Clearly, I meant that if you compare two people at the same weight and height, the one with the lower body fat and higher lean body mass will be smaller.