Overbet -> Spaz Out

This is one of my favorite spots for an overbet, either with a very strong hand like this or with a draw, because Villain’s hand is so clearly defined as marginal showdown value. To be honest, given what he shows up with, I don’t understand why he raised the turn:

PokerStars No-Limit Hold’em, $20.00 BB (5 handed) – Poker-Stars Converter Tool from FlopTurnRiver.com

SB ($3703)
Hero (BB) ($5075)
UTG ($2374)
MP ($2080)
Button ($2000)

Preflop: Hero is BB with K, 5
3 folds, SB bets $60, Hero calls $40

Flop: ($120) 2, 5, 5 (2 players)
SB checks, Hero bets $88, SB calls $88

Turn: ($296) 6 (2 players)
SB checks, Hero bets $377, SB raises to $877, Hero calls $500

River: ($2050) A (2 players)
SB bets $330, Hero raises to $4050 (All-In), SB calls $2348 (All-In)

Total pot: $7406 | Rake: $2

Results:
SB had 10, A (two pair, Aces and fives).
Hero had K, 5 (three of a kind, fives).
Outcome: Hero won $7404

Though I think I’m good 90% of the time on the river, I wasn’t initially looking to get all in. Had Villain bet anything in excess of $1000, I’d have put him on mostly bluffs but I’d also expect to be behind the majority of his value range, so I wouldn’t want to shove. His very small bet makes it look more like he’s got something that can bluff-catch and maybe even is trying to induce a bluff, so I was happy to indulge him there.

It was weird, because he timed down when I shoved, but I don’t know what he was expecting to accomplish with this little bet other than inducing a bluff shove. It’s not like I’m going to play 99 this way and make a crying call on the river. I can’t even have a busted nut flush draw, since the Ac is on the board and the Ad is in his hand.