In most situations sure, the driver who rear ends a vehicle is usually at fault...however, please explain how one is supposed to keep a safe distance when a vehicle, or a**hole biker in this case, cuts into their lane and immediately hits their brakes. The biker's dangerous, and just plain stupid, action allotted no reaction time for the driver to reduce following distance.
Are you condoning the practice of trying to to stop vehicles that weigh 4 to 5 times more than you with your bike? If so, I suggest not attempting to be an MSRF safety instructor.