Edited because I'm an idiot

Your thoughts are good, but I still think Micro's read is key here. I know what he means when after seeing just one signature hand from someone and the time he took to react on decisions etc that you just have him completely pegged. If he says he's passive, he's passive.

And when you include the read and look at the board in its entirety I think quite simply that a passive villain will check a lot of weak made hands on the river for a cheap showdown. I can see an argument for villain betting any ace on the river for value from our K, J, 9 or 7 - if I was villain. A passive villain however is less inclined to do so.

River is bad for our range because the most likely aces in our villain's range are A7 and A9. I'd go so far as to say that the line on every street corresponds most closely with A9/A7 but that is probably overstating the point. Even passive villains bet two pair and sets some of the time, which has to discount the hand combinations that were two pair on the flop (that we now beat) and emphasises the A7/A9 two pair combinations that were one pair on flop when he check/called.

Hands that beat us on the river that we beat on the turn: A9 (9), A7 (9), QT (16) = 38 combos
Hands that we beat on the river that beat us on the turn: K9 (6), K7 (6), J9 (6), J7 (6), 97 (9), AT (12) = 45 combos

The point is that even though we made two pair on the river our hand strength against the range of hands that are likely to make that river bet and subsequently call a river shove was only slightly boosted by the river - not hugely boosted. It didn't change much.

The range I posted is not intended to be 100% accurate but rather to be representative. For every case you can state that he would play occasionally with a ragged ace or similar I'll quote a case where he'd fold AT on the flop or J7 preflop. I think those situations where he sometimes plays exactly like this with a hand that is not listed is almost exactly outweighed by the times he plays differently than exactly this with one of the hands listed. Even though some of these discounts apply to the hands that beat us the line he took chimes most cleanly with the hands that beat us and less cleanly with the hands that we beat.

I've deliberately included hands like J7 and T8o-97o even though you could certainly argue against both simply to provide the buffer for wacky plays from a relative unknown. By this I mean - I've included a lot of hand combinations that could be discounted but we need to be fair and if we discount T8o because he wouldn't even play that, we have to discount 97o, J7, maybe J9o and 97s etc. Instead I leave them in the same way I leave in AT to represent "the occasional raggy ace".