The last live hand is not a winning hand?

When he claimed there was no question he had the winning hand, the other player still had his cards.

When he has the last live hand and we're sure the other player didn't table his... yes he gets the pot.

Tabling half your hand when the other player has a hand is not the "no question" winning hand.

The issue arose AFTER the other player fully mucked his hand. That is when the other players, not involved in the hand, demanded he shows the other 2 cards. At which point he has the only live hand and we have no other players making a claim for the pot.

In every cardroom I have played in, if one player mucks part or all of their hand prior to the other player, then their hand is dead. The second player does not have to show. The extreme example of this is when there was a straight on the board, one player showed pocket queens (playing the 7high straight) and the other player said, "Nice, it's a chop" and mucked his hand after showing a J (presumably pocket Jacks.) The dealer awarded the pot to the pocket Q guy and the floor ruled that the pot must go to him despite the fact that his hand didn't play and even he said that the pot should be chopped (friendly, fair guy.) Rules is rules, you muck before your opponent without tabling, you lose.

HOWEVER, in SOME maybe even most rooms I have played in, if one or more players are all-in by the river, then ANY player at the table has the right to demand that hands be shown face up. The extreme examples of this I have seen are that the player's cards were succesfully retrieved by the dealer even though he tried to mix it in the muck and another time where the hand was killed because he mucked it and it ended up being a chop hand that he lost despite it being tabled after the fact. Players both played the board but he insta-mucked pocket 88 to pocket 99 after the KTTQQ type board.

In the end, you had the right to the pot no matter what because your oppenent mucked his hand first. However, it is likely that your room has a rule that compels you to show all four when your oppenent is all in and someone requests it, so you would have broken the rules by mixing it in yourself. Despite that though, the proper punishment is a warning or a time out and not losing the pot.

I believe you might be intertwining or misinterpreting some rules. Or at least overstating some.