The power of feedback, and I’m saying that without any sarcasm/irony. Most people never get genuine, honest feedback in their entire lives. The people closest to them shelter them and beat around the bush not to hurt their feelings (or the opposite, they intentionally hurt if they are assholes).
But strangers don’t care about your feelings, they can be honest.
Of course they could have been nicer in the story, guy propably had a shitty night and felt bad, but will thank them years later for this moment that transformed his entire life and gave him a different future.