Playing middle pair - Standard river play?

[SuperUberBob]

Villain has only been at the table for a dozen hands. No significant reads.

PokerStars 0.50/1.00 Hold'em (6 handed) Poker Stars Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

Preflop: Hero is BB with T[img]/images/graemlins/heart.gif[/img], A[img]/images/graemlins/heart.gif[/img].
<font color="#666666">3 folds</font>, Button calls, SB completes, <font color="#CC3333">Hero raises</font>, Button calls, SB calls.

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

Turn: (4.50 BB) J[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, <font color="#CC3333">Hero bets</font>, Button folds, SB calls.

River: (6.50 BB) K[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">SB bets</font>, Hero calls.

Final Pot: 8.50 BB

I have a feeling that it might have been best to fold the river. But I thought that villain might be making a move with a middle pp or a ten and a worse kicker.

Does this make sense? Or can anybody here rationalize a fold?