The initial explosion happens from inside the drivers compartment. So, perhaps there were explosives hidden under or inside the passenger side seat that he was not aware of, that was triggered remotely?

If he had been shot in the head, wouldn't his head be slumped forward? Could there have been a mechanism hidden inside the passenger seat that fired a shot through the seat into his head, to make sure that he was dead? And which would then be blown up by the subsequent explosion, leaving no evidence? Although we don't see any sudden movement of his head before the explosion to indicate it being shot, but it does look to me like the head moves from the right to face straight ahead.

We really do need to see the full length video to check.