Also I want to point out, I don't find this surprising at all.
In Japan, I rented a Toyota Aqua. It's suppose get like 40 km/L which is pretty ridiculous. I drove all the way from Narita to Tokyo and back, including driving in the city for two days and the fuel indicator didn't even go down one notch! I did fill up the car before the return and they did not ask for a receipt, but it goes to show with more and more cars becoming fuel efficient, they do need a method to make sure customers pay for gas before returning the cars for very short rentals.