I think it's a shared responsibility thing. The incident could have been prevented by both drivers. Shaun did rejoin the track fairly quickly, but in that corner there really isn't anywhere to go if you're offline. Had he chosen to rejoin the track later, that would have put him either at the apex of the lefthander or in the dip part between the two corners.
Olddog could have either slowed down and fallen in behind him, rather than attempting a pass on the dip, or given him more room.
It's a difficult situation, as in a league race you want to lose as little time as possible, Shaun really could have stopped and let the field past, but he'd just gone from last to third, and I'm guessing the thought didn't even cross his mind.
I'm sure Olddog wanted to take advantage of Shaun's mistake as quickly as possible and make the pass, leading to a rather optimistic pass.
I think it's a racing incident, simply two drivers trying to be in the same place at the same time.