Well I decided to let Pyrebird act for three reasons:
1) Had he invoked an offensive power I'd have allowed him to attack the same round with it. Since he invoked a movement power, he can move the same round with it (which he did) but still has his action to take (which must be something non-flight or wizardry related).
2) If it works better conceptually for everyone, he could've invoked the flight power the round before everyone went charging out the door; I'm sure there was some thought given on the character's parts as to prepping for the coming battle.
3) On a pbp game, the need to move the action along at a reasonable pace urges me to not have players spend a round not doing anything meaningful
So do something dang it!