Yeah, that's definitely true. Google sort of mapped an AWS concept onto its own cluster splits. However, there are enough regional-scale outages at all the major clouds that I don't personally place much stock in the idea of zones to begin with. The only way to get close to true 24/7 five-9's uptime with clouds is to be multi-region (and preferably multi-cloud).

I think also Google as a whole has pretty good diversity. But Cloud customers demanded regions in big population centers and smaller countries where Google traditionally avoided due to cost reasons. This lead to less redundant sites that were often owned and/or operated by third parties. So in the US and Europe you can probably trust GCP zones quite literally. But other regions (I have heard lots of rumours in the APAC) they may not be quite as diverse as they appear.

See: that fire in France that took down a whole region

But on the other hand, GCP supports multi-region so that's not nearly as big of a deal as it would be if AWS zones were not sufficiently isolated