It's rare that they have a total brake failure like that, or maybe he was going for the hydraulic hand brake rotation thing (the R2 class is FWD), and that, or just the rear brakes failed when he pulled it.
The only other thing I can think of is a TOTAL misreading/botching of the pace notes by the co-driver, but the driver could still see the turn coming up (one would think?).
The driver and co-driver may have ended up with some sort of concussions, due to the height and impact/sudden deceleration, but the cage in those things probably saved their lives, being so intensive, and STRONG.