The driver simply takes a tight right hander poorly and understeers right off the road tumbling onto the cliffs below. The side impact airbag goes up immediately showing the level of sensitivity and safety the E46 M3 is built with. I'm not here to chastise this driver as I have done a very similar tumble also in an E46 M3 which gave its life to spare mine.
This video is a reminder that things can get ugly very quickly behind the wheel. It's best to save it for the track and you do not have to be going 10/10's to lose it although this guy had quite a brisk pace using both sides of the public road. Know your road, know your car, know your surroundings, know your limits, and always dial it back more than dialing it forward. If you do not, this can happen and you may not be so fortunate.