Usually Heroku mentions a specific region in any status updates that don't affect all regions. For example, a status update 11 days ago stated "We're currently seeing increased routing latency in the US region. Investigation is underway."

AFAIK this outage only affected dyno restarting (which may have been triggered by a number of reasons) and creation of new dynos. Perhaps your EU dynos were lucky enough to not have done either of these things during the outage?