It looks like the transport rear ended the Chevy and the Mustang broke the straps and rolled over the roof of the transport. Probably held down with straps over the tires and J hooks to the floor. I never did like to see vehicles hauled like that. Just does not look safe and this is a prime example.
That's the arrangement that held Eisenhower's limousine fast when the trailer flipped on it's side, see pic above. FWIW, I haven't been able to discern how it was tied down. In any event, the car shouldn't have come off the trailer. 2ยข
