Flopped bottom straight with flush draw on board

[BB_Specials]

1/2 NL

Hero is button with 7 [img]/images/graemlins/club.gif[/img] 8 [img]/images/graemlins/club.gif[/img]

MP 1 calls
MP 2 calls
Hero calls $2
SB calls
BB checks

flop
10 [img]/images/graemlins/diamond.gif[/img] J [img]/images/graemlins/diamond.gif[/img] 9 [img]/images/graemlins/spade.gif[/img]

SB bets $4
BB calls
MP1 calls
MP2 calls
Hero raises to $20

SB calls
BB folds
MP 1 calls
MP 2 folds

Turn: 4 [img]/images/graemlins/spade.gif[/img]

SB bets 26.70 and is all-in

This reeks of draw so I call

SB turns over 3[img]/images/graemlins/spade.gif[/img] Q [img]/images/graemlins/spade.gif[/img]

River: A [img]/images/graemlins/spade.gif[/img]

SB wins the pot ($128.40) with a flush, Ace high


Is this guy a total donk, or am I missing something?