To be fair, even if it is marked and there should be nothing coming up the inside, the rider should have looked before changing lanes. He simply signalled and went.
Not suggesting for a second that the driver wasn’t at fault- he had absolutely no business coming over the chevrons and into the inside lane. However the rider shouldn’t have assumed there was nothing there- a quick look over the shoulder would have saved him a lot of pain.
The only thing you should ever assume on the roads, is that everyone else is out to kill you, and you can’t give them the opportunity to. Even if everybody on the roads plays by the rules 100% of the time, and never has a lapse of concentration, it can’t hurt to be careful.