Show one, show all rule

[Runner Runner]

I was playing in a small tournament in a cardroom. Hi was utg 4 handed and raised the blinds with A9. It was folded around and after receiving the pot I showed the Ace. One of the players then asked to see my other card claiming it was his right under the "show one, show all" rule. The dealer showed it to him, they both claimed that this was a house rule.

I said that the only way I had ever heard of that rule being interpreted after everyone folded, was that if you showed one player at the table your cards, the whole table got to see them. Has anyone else ever heard of this rule being interpreted as such, or was I just playing at a cardroom that has a house rule that is not commonly used?