Vs unknown I think I'd play it the same. River is meh. Against that sizing you shouldn't be folding much and KQ should still be fairly strong if we assume villain cbets lots of his good aces on the turn. Definitely take a note after the hand though that he's going for thin value with that sizing. Next time it might be more profitable to raise or fold a 2nd or 3rd pair type hand against the thin vbet than to call it.

Well played sir. The turn and river cards are far from great, but given the sizing and how the hand played out I can't really fold this.

I really don't mind folding the river in a passive 5NL game.

If villain wants to bluff then he will almost always take advantage of the ace turn card and fire a second barrel. When he makes such a small river bet it looks like he's wanting thin value and to pot control. It's unlikely he does this with KJ so we're beating nothing from a value range.