If he's gone to a car meet inorder to drive fast down these roads or if this thread can prove in anyway this is the reason for the meet then the insurance company may well try it on, furthermore if the insurance company ask around the people around the road at that time and someone says, "ah yes those guys who had bene overtaking everyone and driving fast".
This thread is an easy source for information for them, if it was me who crashed i would have requested that no photos or videos to be posted, limited chat other than saying someone had crashed and he was ok, actually when i crashed my saxo i requested non of my mates chatted about it on the net until everything was sorted out.
Just thinking how an insurance company might be thinking about this, young driver / high collision road, why was he around that road and what was he doing, it all depends if they want to go down this road, for 10 or so k its prolly not worth it but you never know.
Sorry to bang on about this but i feel its very important to sort out NOW rather than regret it later, why take the chance?
But like you say the situation changes somewhat because you guys hadn't been on the road at the same time etc.
I would also like to say i've been to some of the original meets and other than a chance for mates to meet up and talk about cars and have a nice meal i didn't get the impression at any point or see anyone driving in a manor that would indanger anyone else or himself on the roads.