Unintentional fish

I'm curious to get some responses on this. Seeing as this was a short-handed game, I didn't put him on what he had - I figured him for two overcards and called his flop bet thinking I was ahead (but my bets were hedged with 4 probably clean outs, just in case I was wrong). As it happened I made a pretty terrible suckout on him. Do you think it's justifiable calling that flop bet since I had no read on the player and no real reason to suspect an overpair? Or would you fold that? Also, should I raise the flop if I think i'm ahead here? Since I had the draw I think I was instinctively more passive with a hand I might usually have bet out with, or even check-raised.

***** Hand History for Game 2057879953 *****
$25 NL Hold'em - Monday, May 16, 11:48:24 EDT 2005
Table Table 36591 (6 max) (Real Money)
Seat 1 is the button
Total number of players : 6
Seat 1: groowey ( $25.25 )
Seat 2: BigPerm1769 ( $22.15 )
Seat 4: ernwardo ( $23.45 )
Seat 5: KnightRed ( $39.65 )
Seat 6: KMB_80 ( $22.8 )
Seat 3: stressball10 ( $24 )
BigPerm1769 posts small blind [$0.1].
stressball10 posts big blind [$0.25].
** Dealing down cards **
Dealt to stressball10 [ 5c 5h ]
ernwardo calls [$0.25].
KnightRed calls [$0.25].
KMB_80 raises [$1].
groowey folds.
BigPerm1769 folds.
stressball10 calls [$0.75].
ernwardo calls [$0.75].
KnightRed folds.
** Dealing Flop ** [ 6h, 7h, 3d ]
stressball10 checks.
ernwardo checks.
KMB_80 bets [$3].
stressball10 calls [$3].
ernwardo folds.
** Dealing Turn ** [ 4s ]
stressball10 checks.
KMB_80 bets [$3].
stressball10 calls [$3].
** Dealing River ** [ 7s ]
stressball10 bets [$3].
KMB_80 calls [$3].
stressball10 shows [ 5c, 5h ] a straight, three to seven.
KMB_80 doesn't show [ Ah, Ad ] two pairs, aces and sevens.
stressball10 wins $20.3 from the main pot with a straight, three to seven.