That's because (at same height and weight) muscle mass is more dense than body fat. That's why even though they might be billed same height and weight, Dwight looks slimmer than DJ. Whenever asked: "What weighs more, a pound of muscle or a pound of fat?", a pound is a pound regardless. But when hypothetically asked: "What weighs more, a bucket with a liter of fat or that same bucket with a liter of muscle?", than the answer would be muscle due to it's density.
