Volunteers banning someone with an asshole tendency is not cancel culture. Just don’t be like that. People screw up and make mistakes, no need to insult them for it. The proper way to react is to thank them for fixing it.
One could just as well argue that GP commenter screwed up and made a mistake, no need to instantly ban them with no recourse to even apologise for it.
I don't believe most people in my country would take this as an insult. There are many people from many countries (and subcultures within those countries) with differing degrees of what they will take offense from. From my perspective, the developer perceived a slight incorrectly for sure.
So even if you would have 90% chance of false positive it may be worth it.
At the same time, if you treat them charitable, ignore emotions and do your best with such people/comments, they may also turn out to be great contributors and valuable feedback. Just the fact that somebody takes his time, his most valuable resource, to provide any kind of feedback is something. There are popular projects with known bugs which take a lot of time to reach developers because everybody is busy with their own stuff and doesn't have time to report stuff which others may just as well report. Plus, such person is more likely to share their experience with others which may discourage or encourage some potential contributors like it is happening right now.
It is amazing how much PR can a single person do over the years when she has really strong opinion about something.