I think one of two things likely happened, the rider was thrown to the left, and the truck was in the left lane, but behind both, OR, the truck was behind both and dodged left to avoid the Mustang more than likely suddenly hitting the brakes, and caught the rider in the process.
Of course, that implies that the rider was thrown to the left,... it's possible he went straight up,.. I wonder how fast you have to be moving to manage to wedge a bike in your engine compartment, rather than down it.