I think the LAG player type to go either way on river to be honest. I have seen stranger things in these type of games.
If he puts our hero on a hand like AdQs (Non-spade ace/high-spade kicker) after calling his huge turn bet he could take the As/weak kicker line as a bluff. He bet less than half pot on flop and over pot on turn. A high ace in our range could make sense to this player type.
But either way, we can eliminate the As from his range because we hold it and enable us to make this fold.