I know you're never supposed to pay off a flush draw, but the urgency of his bet combined with his short-stack made me view him as no-flush. He's a donk by the way. Have I simply "fallen prey to one of the classic blunders?"

Party Poker No-Limit Hold'em, $ BB (9 handed) from (Format: Bet The Pot)

UTG+1 ($60.05)
MP1 ($49.50)
MP2 ($31.90)
MP3 ($74.55)
CO ($50.20)
Button ($52.80)
Hero ($60.80)
BB ($49.35)
UTG ($37.55)

Preflop: Hero is SB with , . Hero posts a blind of $0.25.
2 folds, MP1 calls $0.50, MP2 calls $0.50, 2 folds, Button raises to $2.5, Hero (poster) calls $2.25, BB calls $2, MP1 calls $2, MP2 calls $2.

Flop: ($12.50) , , (5 players)
Hero bets $9, BB folds, MP1 folds, MP2 calls $9, Button folds.

Turn: ($30.50) (2 players)
Hero checks, Hero calls $20.40.

River: ($50.90) (2 players)

Final Pot: $50.90