This is a good question.
Player 1 asks to see winning hand of Player 2, as he’s under the impression a winning hand still has to be shown in showdown to qualify for the pot.
The contention that the player has to show his hand to win the pot is simply without base in the rules or logic. If the last live hand standing does not win the pot whom does? Certainly not the player whom mucked his hand first. The guy is winning the pot rather or not he shows cards.
The showdown may be different for tournaments then it is for cash plays. With a cash game there is simply no remedy to award the pot to anyone but the last player holding his hand. Simple argument is that the bluffer mucked his hand thus losing any claim to the pot. The remaining player gets the pot.
It is not clear rather player A asked to see the hand or not, or if he did, rather or not the hand was in the muck already. Player 1 can ask to see the hand but it has no bearing on how the pot is awarded. Once a hand is in the muck, player A cannot see the hand, or in other words the hand is not to be retrieved from the muck. It is a done deal. If he did ask to see the hand or there is a rule that winning hand at showdown needs to be shown, it is up to the dealer to protect the muck and turn the cards faceup. If the dealer fails to do this it does not mean the pot is up for contention. It is a minor thing and the game moves on.
I do believe some tournaments require a winning hand be tabled at showdown. Even so it will not change anything as far as awarding the pot. Player 1 still mucked without showing, which is conceding the pot, which means he has no claim to the pot. The one difference that may apply for a tournament if they have winning hands must be tabled at showdown, is that the tournament director may be able to penalize a player for ignoring the rule, with sitting out a round or whatever.
The way the OP described the situation player one was taking a really naïve shot or a long shot to win the pot. IE he was making a really stupid angle. If I was making a ruling on this I would tell the dealer to push the pot to player 2 and deal the next hand. If player 1 wanted to complain I would tell him he can talk to me away from the table, than I would walk away after spending ten seconds to much on this decision. If player one wanted to hold up the game, I would threaten sanctions. He is just taking a shot and I don't think he should be allowed to hold up the game.