Ruling?

[DrewDevil]

Last night I was playing in a 2-5 NL game.

I had position heads up, and while I don't exactly remember the cards, I pretty much had the nuts and I was planning to bet the river.

With the action on him, the other player sort of mumbled something that sounded a little like "check" but I really couldn't make it out at all.

So I said "Check?" in a way that it was unmistakably a question. The other player immediately flipped over his cards and the dealer said we both had checked.

I won the pot, and the guy may have folded to a bet anyway, but do I have any argument that I wasn't checking behind and was just asking?

The