pedal power

While waiting for a bus one morning last week, I saw (across the street) a man with one foot, on a bicycle. I guess he was pushing along the ground with his one foot; I spotted him as he came to a stop. Having stopped, but before dismounting, he took a dummy foot from a bag and prepared to install it on his stump. Why didn’t he put the foot on and use it to pedal? I imagine that would be easier than walking with it, and more effective than riding without it.