The resistance element of cycling means that it doesn't just burn fat: it also builds muscle - particularly around the glutes, hamstrings, quads, and calves. Muscle is leaner than fat, and people with a higher percentage of muscle burn more calories even when sedentary. To be clear - you won't end up with quads like a track sprinter unless you invest a serious amount of time at the squat rack. But you will develop a nice toned derriere.