So this affected devices even using the updated DNS servers 156.154.70.1 or 156.154.71.1?

FYI, best practices for deploying DNS servers is to have them different subnets (which it appears have been done) and geographically or logically different network paths than the primary. If a single switch took down both of your DNS servers, then something should be done to resolve this issue, otherwise, when an unscheduled outage happens with that same switch, the same thing will happen again.