The reason to bet the river isn't so he'll call with worse, it's too induce. We're hoping he weights our range towards what we have and shoves a range that is unbalanced towards bluffs here. I'm quite surprised he showed up with A4s, but seeing that he did makes us way ahead of his range after he checks the turn, so he doesn't need to bluff that with many of his hands in order to make this profitable.

As for whether we like his jam...meh, depends what he thinks of you, but erring on the side of no after recent AK hand...he must know his own image. Looks to me like he called preflop with the intention of trying to bluff you postflop at some point regardless and wanted to get the last bet in, which could be why he didnt bet the turn when checked too, because then he might lose the battle of the air if you C/R?