Accidental muck rule

In a game this evening, the cards from my hand hit the Board cards when I turned mine face up and dropped them on the table after all action was completed. The River betting was heads up, and mine was the winning hand. I had already called the last bet. In fact, I tried to raise it, but then the Dealer informed me the last bet had put the other player all in, and she said "Show them."

I was sitting across the table from the Dealer, who was spreading the Board cards unusually close to me because of the location of the cover over the shuffling machine. When my cards touched the Board, the loser started yelling, "Muck, muck," and was furious when the Casino refused to rule my hand dead.

It doesn't seem possible that the winning hand could ever be ruled dead under such circumstances, but I don't know whether the Casino was just being nice to me because the other guy was such an obnoxious sore loser. Does anybody know the rule on this? Thanks.