> He's engaged in a petty argument with the driver
No; the argument occurs outside the vehicle, and is with the driver's partner. And it is not so much of an "argument" as him being repeatedly provoked with statements such as "You want to come at us? I say go get yourself some lunch, big boy. Go ahead."
> tries to block her car with his body
No, he does not. He happened to move around the front of the car, which is consistent with circling the car to get video footage of it from all angles which would be part of expected evidence-gathering protocol. The car can be seen (including in other video) to move back and realign as he is walking in front.
> then says "fuckin' bitch!" after he's killed her.
Even left-wing sources like the CBC concede that "It is unclear who said those words."