Well he re-raised preflop so he either has a biggish pair or overcards. He can't have the flush on the turn because if he flopped a flush draw in position after re-raising preflop, he's surely betting it, he can't have a set because no way he gives a guy like Xas who could have any two a free card on that board and same goes for overpairs.

Since he can't have a made flush, set or overpair on the turn his most likely hand is most likely with a K or Q kicker.

The river bet confirms that he doesn't have an overpair or set (one card straight and made flush out makes it unlikely to valuebet even a set here I think) so he's either got the flush (nuh-uh) a straight (nuh-uh, he can't play 88 like this) or Ace high for a busted draw (yah).

At least that's how I guess Xas was reasoning. Makes sense.