Where was the monk Positioned? I would figure the dragon-then-fly would be positioned where the Middle of the dragon would be.
The monk couldn't have the reflexes to grab the fly, if the fly was even 10 feet away. There's nothing for him to Jump off of, he's free falling. If you think he can move ten feet with nothing to push his weight off of... then somehow, we have a flying monk.
There might've been like... No trees, cliffs, walls, etc? He went right into the sky.
Besides, the dragon likely had a higher Con. It could've taken a Deep breath, and kept flying up, until the air thinned. When Monk starts loosing air, the dragon just shakes him off, barrel rolls, etc.