So the bike and the car were playing silly buggers BEFORE the accident, but eventually the bike got clean in front of the car and then lost control? Or lost control trying to pass the car?
Bikes are entitled to filter past stationary or slow moving traffic, but it is their responsibility to ensure that it is safe to do so. Knowing that the car had already overtaken him once, presumably out of revenge for being passed by the bike, the biker should have exercised caution passing the car a second time. Providing the car didn’t do anything silly like moving to the right to teach him another lesson as he tried to filter past, then the car is not at fault, though should probably show a bit more respect for other road users in future.