That’s kind of weird. It’s not that Siri is especially bad. It’s that “Siri” is something different depending on how you query it. Other online search systems aren’t like that, and integration and consistency are typically Apple’s forte.
Look, I'm not arguing it's not a bug, but I'm just really surprised at how software people, who I think should know better, are surprised that such bugs exist, or more importantly that completely eliminating all types of this class of bugs is basically impossible with current technology.
Half the time, Siri replies with "I'm sorry, you don't have an app for that. You can try searching for one on the app store."
Repeat the same exact query to the AirPods seconds later, and bam, it starts the workout on the Apple Watch.
The aspect that's ruffling feathers, I believe, is that it's one of those cases where someone might have reasonably assumed something was built one way 'under the hood', and was confronted with an effect which forced them to see that it was not implemented that way at all. The issue isn't the 'bug'. It's the realization that their mental model was wrong.
Specifically, something has a name ("Siri") which might lead one to believe that everything from that manufacturer using that name refers to the same thing. (Isn't that the point of a name?) Clearly, it's not.
Your hypothesis sounds plausible, so I tested it. I have a Mac laptop, which has the same 'Location Services' that iOS has (AFAIK). I asked Mac Siri what time it is in London, and got a response for the one in England (further away from me). So that doesn't explain it, or at least not all of it.