it's just for entertaining

Everyone knows Prius uses less gas under normal conditions. But you should be aware that this video is from a TV program called Top Gear, in which the guys do extreme things about cars.
The bottom line is, this test is fair as both cars are going at the same speed. In terms of how useful this result is, that's another story. But at least their conclusion is ultimately true, that it's how you drive, not what you drive.
My guess is the prius was at full acceleration whenever possible and used max break in corners, while the M3 didn't even have to break during most corners because it handles better.