I have watched the video from two different angles, this is what I think happened. He was hard on the hand brake, when you do this the low air pressure in the tires can cause the back of the car to start bouncing, which his did, in my opinion he new what was going on and was trying everything too stop. But it bounced at the wrong time and he cleared the sand trap and went right into the retaining wall.
If you look at how many runs are made each year, this is a pretty safe sport. I agree there is always room for improvement, but at the speeds they are going they have done a good job.
Ken