Do they have an official description what a zone is somewhere?
Back in the days when we had our own data centers a zone was defined as a "fire section" meaning that it should not be impacted if any other zone of the data center had a fire. This obviously means that you can't call 3 floors of a building a zone.
Edit: The information on this site https://cloud.google.com/docs/geography-and-regions#regions_... clearly states that a zone is "physically distinct" so they have some explaining to do.
Edit 2: Sneaky... They changed the status page to say "europe-west9" instead of "europe-west9-a".