Usually, when you have a fender bender, both parties pull over to the side of the road to sort out all the insurance information. Never have I ever seen those two parties just keep on going, like the mating of a pair caught in eternal bondage and bliss.
The driver who filmed this seems to really just capture the only appropriate reaction, at the end of the video:
The video description expands a bit upon the "what," but a full explanation is still somewhat lacking:
This lady cut off a cement truck and I watched him rear end her. When I noticed that neither vehicle came to a stop after the accident I started to record...
The car being rear-ended seems to hit the brakes a few seconds after they pass out of view of the camera, but even still, that seems like the world's most delayed reaction. Maybe we'll never know what the hell happened here. Maybe it's better if we didn't.