superheating is rarely a thing and you can avoid it in a multitude of ways including slapping a spoon in your cup
It's not worrying at all unless youve never used a microwave for this purpose. I've microwaved a shit ton of water in those exact Pyrex measuring cups and never had an issue with superheating. Nobody in my family ever has going all the way back to the 60s.
The variables involved in driving are not reliable. Even if you're the safest driver you can still be involved in an accident. The same cannot be said about repeatedly boiling water in the same vessel for years, like the person you are responding to. They are not lucky in the same way drivers are to avoid accidents.
They'd not experience this situation as, like another commenter stated, even a pyrex glass has nucleation sites for boiling
If they've double-microwaved the water then they have a chance at superheating, but that is not the same situation as just microwaving water in a pyrex cup, the thing that was being called extremely dangerous
But sure, well just keep being scared of doing it at all because some people can't remember that they already heated something