The truck did not brake until an instant before impact
the truck never even began to swerve into the empty left lane, even after impact!
The rider saw it coming. You can see him start to stand up almost as if he is going to jump away. As fast as the truck was moving, I doubt if he would have had time to dump the clutch and try to shoot out of the way. Most riders in that kind of accident suffer really bad spinal injuries.
When sitting at a light like that, I watch the mirrors and tap the brake lights at a constant blip every half second or so. If the approaching vehicle shows no signs of slowing, I will start the process of engaging the clutch and revving the engine for a quick getaway.