That brings back memories of my crash. *shudders* I didn't see how it happened but there were easily a dozen people involved, maybe more; I didn't pay attention to who got up and rode off after I crashed. All I know is that fast riding, pacelining, lack of communication, and not looking before moving to the left factor into the incident. There might be more but as I said, as soon as I was involved, the rest of the fallen faded into the background.
That's a shame about the guy with the broken hip and the others who didn't get up. I feel for them.