there was another site that linked to this, he said he was compiling a video of cliff diving, stunts, etc, and this was just one of the stunts and he ended up getting sideswiped...
Rich - it's a game - Grand Theft Auto. You can get points and impress your friends by doing "insane stunts." Apparently he intended to drive the ATV off the cliff but got sideswiped instead. The airplanes and other traffic show up rather randomly, so it's quite a coincidence that his stunt got ruined that way.
I'm going to go do something productive now in order to make myself feel better about knowing all of that.