Actually sounds like a layer 2 design
They talk about a "broadcast storm", but it sounds more like it was a faulty switch sending continuous spanning-tree updates.
10 years ago, had the same thing happen on the last major Layer 2 campus I did. Same situation, down to one faulty switch that needed to be disconnected to stabilise the network, then replaced. Don't ever believe the error detection and update suppression mechanisms work. They don't.
Put me right off, and I only design layer 3 environments now, far more stable and reliable.