Also, I thought there was very clear guidance about not discharging guns towards unarmed drivers as it doesn't tend to stop them and is likely to result in the vehicle being accelerated into someone/something.
One reason would be that after the first time he fucked around and found out with a vehicle, he resolved to shoot the driver the next time. This would explain why he tried to box in the metal car with his squishy body while keeping an exit strategy - being positioned at the right place to claim he was worried about being hit without actually getting hit. It would also mean this incident was premeditated murder.