I agree with Bill,
In an All-in Situation, a defending player with a set of Queens on the flop will almost each time put all his chips in the middle. The fold ratio here is not significant to be considered.
Plus, there are 2 witnesses saying they heard call.
Players should protect their hand until they receive the pot.
The focus of the above view is on what Player 4 did. Equal if not greater focus should be on what Player 1 did, i.e. was it reasonable? If he
and the dealer both heard "fold". Forget Player 4's hand as that is not relevant to whether an unmistakable call or fold declaration was made. Looking at the hand and asking "would I have called in that situation" is a real slippery slope.
1: Two heard fold including the dealer, Two heard call. We cannot say with certainty a call was made. We can say "well I would have called with a set of queens". But what if 3 straight diamonds were on the board?
2: Meanwhile a player who made an all-in bet has mucked thinking it was a fold.
3: Only one surviving hand, we can't kill it because we're not sure if he called or folded.
4: Player 1 did muck his cards prematurely, unfortunately, but should this cost him his stack if the call isn't certain?
5: Pay the surviving hand the pot that has been called with certainty.
6: Here's another important twist: Given the circumstances, if Player 1's cards are still identifiable or if Player 1 had tabled his cards, would you force a call on Player 4 here? i.e. the two adjacent players say "I heard call" and dealer and Player 1 say "I heard fold". There's no certain forced call. Now that Player 1 doesn't have any cards, it's convenient for Player 4 to say "I called" since Player 1 has no cards.
What if Player 1 insta-tables a flush, are you binding Player 4 to a call here considering the dealer heard "fold"? I doubt it. If you won't force a call on him when Player 1 has cards, why would you decide with 100% certainty he calls when Player 1 doesn't have cards?
Interesting case and conversation, thanks!