My understanding is that you are required to give way to a rider moving up the track if they are overtaking a slower rider (always overtake on the right of a rider). So the clown with the disc wheel should have moved in unison with the rider below him as he moved up. I am probably wrong though.
But I still think Mr. -4kmh should of pulled right off the track so those behind him didnt have to make such a sudden shift up the track to avoid him. I mean if you have blown your doors off why not get as low as possible and stay out of the farken way?