From the information available publicly, it's obvious the issue was him airing his grievance publicly.

But being banned from YC is a fairly extreme measure - especially for an activity that has a hint of moral impetus.

Both 'skipping vaccine lines' and 'immediately naming and shaming private conversations to the entire world' are kind of selfish and toxic signals.

If I were the King of YC I would have had condescending words with both of them and told them to grow up and then that would be the end of it.

Note however, we don't really know what happened behind the scenes.