If you show one person your hand? Do you have to show all?

[AncientPC]

There were only 2 people at the river, and afterwards they showed their hole cards only to each other but not to the rest of the table. There was no showdown, one of the guys folded.

I thought once you've shown one person you need to show the table, but he said that since it was the only 2 people left in the hand they didn't need to show anyone else.