You'll never know the cause.

"Driver error" of course is going to be a factor to most people, in that it was an error to put two wheels off the tarmac at that speed, but at the end of the day, thats what happens when the adrenalin is flowing, you make a quick decision, and sometimes they are good ones and sometimes they are bad ones.

Id personally class it as simply bad luck, its the sort of thing that happens to us all from time to time when we are driving on or near the limit.