The report I read said the curbing broke. It did not specify if it was previously broken or if the car broke it. Either way, the nose pitched up and that was enough to achieve actual flight. These cars are essentially flat bottomed airfoils all the way back to the diffuser, so they are especially intolerant of a positive angle of attack. It's like an airliner picking it's nose wheel off the ground and then taking off. The curbing didn't actually launch the car, but it did pitch the nose up enough for the car to take flight.
Instead of having track limits controversies, curbing breaking cars or pitching them into the fence maybe it's better to put the grass back in and they either deal with it or they wad the car up on the wall.