K5o - my bluff hits but wtf?

[Roy6]

Villain is 55/18

Villain limped on the button. With these stats I think he has trash. That said he might peel with T7s, so maybe the flop bet was a mistake.
Do you call down after the turn raise?

Party Poker 5.00/10.00 Hold'em <font color="#0000FF">(5 handed)</font> link

Preflop: Hero is BB with 5[img]/images/graemlins/diamond.gif[/img], K[img]/images/graemlins/heart.gif[/img].
<font color="#666666">2 folds</font>, Button calls, <font color="#666666">1 folds</font>, Hero checks.

Flop: (2.40 SB) 6[img]/images/graemlins/club.gif[/img], 3[img]/images/graemlins/heart.gif[/img], 8[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets</font>, Button calls.

Turn: (2.20 BB) K[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets</font>, <font color="#CC3333">Button raises</font>, Hero calls.

River: (6.20 BB) 9[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">Button bets</font>, Hero calls.

Final Pot: 8.20 BB.

[Spicymoose]

Another tough one. I think he could be semibluffing you, so I think a call down is in order.