Ive done stuff like that before. It's seems to be the insanely low gravity and being bumped from underneath causing a huge boost to the car's velocity.
This actually makes me admire the effort the developers had to put into games to make them even playable on the psone given how weak it was.
You could almost see a 32bit Grand theft auto 3 in there somewhere. Maybe. The pop up is pretty dreadful though lol
I also liked messing around in Driver. I usually made a ramp out of other cars (they stopped driving completely when you hit them) and used it to fly to places.
I think the Gta3 pop up is a little less noticeable though. You can see the entire city at any one time albeit a very low poly version of distant areas. Also Rockstar don't seem to care about frame rates much.
You can even see from that Driver video that entire blocks of buildings just appear. But it remains pretty smooth throughout.