Anything can happen at an autocross. Being a part of the sport since 1981 I have seen many incidents. My wife broke her back in a parking lot event at 25 mph in Jax.
I looks to me the driver carried alot of speed into his final turn, and did not modulate the throtle as he did perviously, and kept the steering wheel turned to the left. Add to that, it turned over on the drivers side in a light weight car.