I think u just need to think about which hands ur opponent will do allin on so scared board. But i think, that mistake went from the preflop from your side. Why u made call with KQo? U want to give freecards for opponent, who just tried to steal bigblind?
Now let's think about opp's all-in's call range: in this spot the best hand for you, which he may have - A-high flush draw. He could catch straight with JTo, 999, 65s+. U beat not so much, so it's seems to me, that best opinion was to fold on his flop 3-bet.