Something similar happened to me a couple of years ago. I'd been for a night out with a group of friends in Liverpool. We were waiting for a train on a freezing cold platform, in the dead of night. I thought that we were the only ones present and started singing. At that point a new voice joined in - a rather enebriated Scouser (how unusual for Liverpool where, of course, alcoholic drinks are practically unknown!!). The singing carried on, on the train, with other passengers joining in. The repertoire was mainly confined to Irish rebel songs but it was still one of those 'magic moments' referred to above ...