It's not the karma: I can see Gleb's post on Brussels with a lower score and a lower %, but not that post. (When not logged in I can't see the Brussels post.) Probably it was "deleted." That is a state where the permalink continues to work, but the post does not appear on various indices. I think that if the author or moderator wants to break the permalink, they have to click "ban." Deleting an account does not delete all the posts, at least in the past.