Here's a couple of more. The first one shows the piece of metal on the ground, angled up toward the bike - easy to see how it could get into the spokes.
This second one appears to show the metal object in the spokes:
This shows the blades sheared off even with the rim:
Almost looks like a windshield wiper blade Not much of a piece of metal to cause such a catastrophic crash:
Bottom line: this is one of the risks of riding fast in a tight group. You are essentially riding blind and relying completely on the leader to warn of road conditions. I wonder how the leader of the group missed it and failed to warn everybody?