All we have is assumptions. What it looked like to me, was that the cage was pulling into the left lane, saw the bike that was running the video, approaching fast, and moved back into the right lane to let him pass. The bike in the right lane was approaching way too fast, and tried to pass the car on the right as it was coming back into the lane. So far, no one has broken a law or started anything. When the bike on the right hits the BMW, that is where it really starts to spiral into total idiocy.
The BMW driver was an idiot for pursuing them, the bikers were idiots for assaulting him. The bikers were guilty of assault, and, many places that woman would have been within her rights to shoot to save her (husband?)
Yup - a whole crowd of idiots, gathered together on the road, each trying to show the others who is the most stupid of the bunch. If any of them had just let it go and kept riding, none of this would have occurred. Instead, folks, if identified, may spend time in the slammer for letting their egos make serious decisions, rather than their brains.