Looking at the first part the "bruv" in the car pulled out infront of the biker, the biker beeped his horn, you then hear the wheels spin in the car, he saw the biker but just though he would pull out and speed off anyway. So he knew he was in the wrong coupled with the beep on the bikers horn, the "bruv" in the car thought the biker was giving him grief so "bruv" then flips the finger at the biker. As for the bikers actions- well hes a biker innit bruv, maybe bruv wont be so quick with his middle finger next time.