"That in turn led to a “thundering herd” effect—triggering a failure of our DNS system." I'm just a spectator but I can not imagine that this was somehow caused by a DNS failure.
I’m not sure I can even count the number of outages I’ve been involved in that had DNS issues as at least part of the cause.
Another give away that this is a lie is that support emails were getting a stock postfix error message which means that MX records at least were resolving.