I am not sure whether this is funny or dangerous:
But it seems the guy found a way to fool the mileage logged in the odometer.
Way back during the oil crisis, a friend of mine used to that on his parents' Volvo station wagon. It had an automatic transmission. Lets say that the car developed a bad case of transmission problems a few years afterwards.
Thinking back, it was quite dangerous coasting on highway 123 without the engine running.