If each request simply came from the same IP address then yeah, all the recipient has to do is block that one and the whole attack is over.

But what if piracy websites were trying to stream content directly from the internet archive rather than make a copy of it first, and messed up to cause this attack. So intentional to cause the traffic but unintentional to cause this amount of it. Or even if those websites first opened the door, and then someone tried to DDoS them, which propagated onwards to the internet archive, whether knowingly or otherwise.

Anyway, I was just postulating that it was theoretically possible... and odder things have and continue to happen all the time so who knows?:-P