Marshalling is, in my opinion, somewhat of a grey area. It shouldn't be I know. Some people say the first priority is the marshalls safety. Well, If you're in 8th off road or large scale it most defo is, but as for 1/10th off road, it's the first car that crashed, then the next one and so on.
I've been in races where the marshall is too busy watching the race to notice which one crashed first, which is frustrating to say the least.
Your dude should have been paying attention. Simple as that, nothing can be done, so I'm afraid it goes down to a racing incident