Your friend would be better off stating that walking is superior to cycling because when walking you have to support your body weight whereas when cycling you are in a seated position. Regardless, the calorie burn from cycling is far higher than walking, whether you pedal & coast or pedal continuously. And what if you didn't coast? What if you did intervals & went at your max for 5 minutes and then recovered by pedaling lightly for 1 minute, rinse & repeat... are you still cheating? I prefer to pedal continuously as it's flat where I live but I still vary the cadence & power so I am constantly either tiring myself or recovering.