I'm guessing it was something lower level than Kubernetes/Borg, since it was able to affect all of their networking bandwidth across multiple regions. ¯\_(ツ)_/¯
The interesting tidbit in here (really the only piece of information at all) is that the outage itself prevented remediation of the outage. That indicates that they might have somehow hosed their DSCP markings such that all traffic was undifferentiated. Large network operators typically implement a "network control" traffic class that trumps all others, for this reason.
