My thinking is very very likely to be completely wrong here since I'm a low level player, but here goes.
Button min-raises, possibly as a steal or to induce a bluff. Hero is either restealing or has a decent enough hand to call a raise here and instead re-raises to become the pre-flop aggressor. Now the fact we have no info on Hero, BU or BB makes this a little harder so without that info Hero could have anything from a low pocket pair, to hands like low suited connectors, or even something like AKo, KQo, maybe as low as K4o or something else fairly weak that makes a strong hand for restealing.
BU calls, Hero knows BU is likely to have a fairly strong holding here unless BU is fairly passive.
Flop comes K♣ 2♠ A♠ - Hero checks, once again this doesn't really do much to narrow things down that much, but it does help a little. If Hero connected with the board with an A, K, or two spades he's likely going to cbet to protect his hand and/or for value. He might check here if he missed completely since this is quite a wet board. BU checks too.
Turn comes 3♠ and Hero bets into BU. I think this could be a semi-bluff here, maybe with some :spade:, hoping to scare BU off his weak holdings. BU calls, so Hero may put BU on some kind of monster hand that was slow-playing the flop, maybe two pair or trips that saw through his bluff on the turn.
River comes 8♠ and gives Hero the
he needed making him a flush. It's possible BU also had a spade here but we think he had two pair or trips, so that rules out the 2 or A of :spade:, meaning the only card that could make him a threat here is K♠.
BU bets the river, unless BU is very keen to make bluffs all the time, it's likely he has a K♠ here or another high
and Hero's thinking earlier was wrong. BU may have checked with suited connectors, 4,5 and made his straight or a weaker flush on the turn. There's also a chance he could be bluffing still. The odds are good enough and Hero shoves the river hoping to get a call from a worse hand.
Hero turns over Qx T♠ showing he was also looking for a straight too.
--- Just some fishy evaluation there, and wanted to go a little off-track from the other thinking in this topic to give myself some +EV based on the fact most of my initial guesses were already taken. ♦