fold with pocket aces on river...dumb?

[bank]

Party Poker Pot-Limit Hold'em, $2 BB (8 handed)

UTG+1 ($95.15)
Hero ($100)
MP2 ($397.40)
CO ($97)
Button ($80.95)
SB ($130.60)
BB ($360.60)
UTG ($602.50)

Preflop: Hero is MP1 with A/images/graemlins/heart.gif, A/images/graemlins/spade.gif.
UTG calls $2, UTG+1 folds, <font color="CC3333">Hero raises to $9</font>, MP2 folds, CO folds, Button folds, SB calls $8, BB folds, UTG folds.

Flop: ($22) 9/images/graemlins/diamond.gif, 9/images/graemlins/spade.gif, Q/images/graemlins/diamond.gif <font color="blue">(2 players)</font>
SB checks, <font color="CC3333">Hero bets $20</font>, SB calls $20.

Turn: ($62) J/images/graemlins/diamond.gif <font color="blue">(2 players)</font>
SB checks, <font color="CC3333">Hero bets $20</font>, SB calls $20.

River: ($102) 7/images/graemlins/spade.gif <font color="blue">(2 players)</font>
<font color="CC3333">SB bets $55</font>, Hero folds.

Final Pot: $157
<font color="#990066">Main Pot: $102, won by SB.</font>
<font color="#990066">Pot 2: $55, overbet by SB.</font>

Results in white below: <font color="white">
SB doesn't show.
Outcome: SB wins $157. </font>