You're seeing monsters under the bed, pod
I would fist pump 3bet this every single time until I knew specifically that a 5x open from this player meant a huge hand. The way I see it, this "bad lag" is putting extra 2bbs of dead money in the pot on a steal and I'm more than happy to take it.
But since you flatted your line is probably best postflop. He seems too passive to valuebet own himself with a worse ace so might as well help him out
Although he did pot it on the flop so just because of that C/Calling seems viable as well. There's not much of a decision left on the river. He will often snap call with any ace thinking it's a split now so just shove.