They're both similar and very clever, but they do operate differently. Sleep sort works by setting up a delay and callback based on the values that you are sorting, so timing is crucial. The solution in this topic is using the network as a queue to store values and is constantly throwing them back, only pulling them into the sorted stack when they reach the max threshold. Once an item is pulled down, its value is recorded and isn't echoed out again. The process is repeated until the list is complete. This works without regard to timing.

"Once COUNTER reaches 1000000, you have all of the values stored in the incessant stream of ICMP requests"

This sounds to me like...

https://en.wikipedia.org/wiki/Delay_line_memory

It's complicated by the fact that ICMP packets do not necessarily arrive in order.