The Talonflame could have had the Ability Gale Wings, which gives priority to Flying moves when it's at full HP.
However, it's also possible that the Talonflame had a Speed-boosting nature and a Choice Scarf. 252 Speed, +Spe Nature, and a Choice Scarf puts Talonflame at 579 Speed. As Dragon Dance boosts Speed by one stage (1.5x), your 383 Speed Dragapult would've had 574 Speed after one boost.
I suppose Talonflame is deceptively fast.