When the "Señores" pretend to sing at Mrs. Bixby's party with Alice singing behind the curtain, just before Signor Spumoni exposes them; Señor Gusto stops playing the flute, yet there is a flute playing the scales just before Señorita Cucaracha is exposed. Not only that - but it is not off-key at all (the flute plays just as it did on the record).
At the party, Moe is pretending to play a black flute, which is nickel-plated and produces a somewhat deeper sound than the standard flute which was used on the recording made at the station.
When Signor Spumoni arrives at the party he tells Mrs. Bixby he can't play his fiddle because the Spaniards busted it. In fact, Spumoni busted the fiddle over Señor Gusto's head during the melee at the recording studio.