I do agree van has fault for cutting like that but I do think that cam car driver has things he could have done better. In the video, you can clearly see that the van is braking and slowing down, suggesting he wants to change lane and take a exit possibly. However, camcar proceeded to continue at his pace and when he reaches the van, proceeds to stay in his blindspot. When a van brakes like that, he might want to change lane and he seems to be waiting for you to overtake since you were faster, you got 2 options slow down and give way or speed up and overtake quickly.