He was not complying with the order to exit the vehicle. He delayed as much as reasonably possible while talking on a cell phone. He was non-compliant for that duration.
When the doors were opened, he put his leg out of the door. But made no effort to get out in any way. None.
Watch the video again.
He wasn't using his leg to stand up, he was using it as leverage to remain in the vehicle. (Ask any wrestler, without the leg as a point of support, it would have been easy for the police to pull him out.)
One officer decided enough was enough, and yanked him out despite his non-compliance. That was not a easy task, this was a fit top NFL player... who then responded, in shock, "Damn..." Watch it again. It's not difficult to see.
Hill was not voluntarily exiting the vehicle. He was trying his best to stay in the vehicle and delay.