The thundering herd problem is more like, there's a hundred cooks, one griddle, and only one of them can make an acceptable waffle for the customer.

This specific problem we're discussing, of concurrent client retries effectively launching a self-imposed DDOS attack, isn't exactly the thundering herd problem. It's clients and servers instead of threads, for one thing. But it's a good enough analogy to another type of cascading failure in concurrent computing, IMO.