Was this fold with KK the right move?

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Im thinking he either flopped a set, had 910 or QJ. But maybe he had AQ KQ, im not sure.


Full Tilt No-Limit Hold'em, $0.10 BB (6 handed) Full Tilt Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

UTG ($4.50)
MP ($14.25)
CO ($15.65)
Hero ($9.55)
SB ($8.80)
BB ($1.90)

Preflop: Hero is Button with K[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/heart.gif[/img].
<font color="#666666">2 folds</font>, CO calls $0.10, <font color="#CC3333">Hero raises to $0.4</font>, SB calls $0.35, <font color="#666666">1 fold</font>, CO folds.

Flop: ($1) J[img]/images/graemlins/spade.gif[/img], 2[img]/images/graemlins/heart.gif[/img], 8[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
SB checks, <font color="#CC3333">Hero bets $0.7</font>, SB calls $0.70.

Turn: ($2.40) Q[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">SB bets $1</font>, Hero calls $1.

River: ($4.40) 5[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">SB bets $4.2</font>, Hero ???