$25 NL KK called down on FLSH DRW board by solid player and donk

[FearNoArt]

PokerStars No-Limit Hold'em, $0.25 BB (9 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

SB ($34.95)
BB ($25)
UTG ($23.45)
UTG+1 ($18.60)
MP1 ($14.80)
MP2 ($35.65)
MP3 ($17.95)
Hero ($65.45)
Button ($13.40)

Preflop: Hero is CO with K[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/heart.gif[/img].
<font color="#666666">4 folds</font>, MP3 calls $0.25, <font color="#CC3333">Hero raises to $1</font>, <font color="#666666">1 fold</font>, SB calls $0.90, <font color="#666666">1 fold</font>, MP3 calls $0.75.


Flop: ($3.25) 2[img]/images/graemlins/club.gif[/img], J[img]/images/graemlins/diamond.gif[/img], 8[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, MP3 checks, <font color="#CC3333">Hero bets $2.75</font>, SB calls $2.75, MP3 calls $2.75.

Turn: ($11.50) 4[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, MP3 checks, <font color="#CC3333">Hero bets $8.5</font>, SB calls $8.50, MP3 calls $8.50.

River: ($37) T[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">SB bets $12</font>, MP3 folds, Hero ?



SB is a tight/solid player (16/3/2 250 hands) His calling of my near pot size bets has me confused, surely he'd re-raise with a set, especially with MP3 being a fish (73/2/1) and calling down hands with any pair/draw. What can villain (SB) have here ? MY image is def TAG (13/10/7 90 hands) and have have won with solid hands.