Is this really relevant, though? To the users who were unable to use their browsers normally it doesn't matter that this problem could have occurred elsewhere as well, but rather that it did occur here in particular.
If particular sites would break, then that could be debugged separately, but as it stands even people who'd be perfectly fine with browsing regular HTTP/1.1 or HTTP/2 sites were also now impacted, not even due to opening a site that they wanted to visit themselves, but rather some background piece of functionality.
That's not to say that i think there shouldn't be telemetry in place, just that the poster is correct in saying that this wouldn't be such a high visibility issue if there was no telemetry in place and thus no HTTP/3 apart from sites the user visits.