[Mr Rick]

Of course you should never throw in your cards before your opponent shows regardless of what he says. I have heard people clearly say "Flush" when it is their turn to show and then when I make them turn their cards over they have a pair. They then say "I was thinking you had a flush"...

If it will make you feel better, he likely did have a flush in order to call your all-in and wanted a diamond because it would be less likely to pair the board.

I have no idea what the rule is at Foxwoods about miscalling your hand but it would be hard to prove with certainty so the guy would probably just get a warning if the Floor was called. But the Floor only gets called in these situations if the guy has to turn his cards over and somebody discarded their hand into the muck and its still retrievable.