as someone who has seen alot of accidents (ie: tow truck driver on the Jersey turnpike), i'd say he tried flying down the access road, hit 3rd (had to be going at least 80) and lost the back end. from the looks of the pics, the Silverado and Ford had a parking spot between them from the fluids on the ground. that guy was FLYING when he hit!!!
no matter how that happened, OUCH!
reminds me of a Vette at E-town making a pass on a windy day. as soon as he got past the stands, the car caught a nasty wind and went over on it's roof.