Thing is, this truck had no reason to be on that stretch of road. It's odd as the road can only go to Durban along the coast and is not great for large trucks. There is also no toll to avoid, so what was he doing there.
Also, the sheer momentum and velocity to have caused the damage to so many vehicles and still flip at the end is phenomenal. This is not a brakes failure, this is either deliberate ( suicide ) or throttle failure where it was wide open. No way a geared down truck will have that much momentum.