You can't really tell in this pic, but those flying units are called Brood Lords. They're made off of Corrupters (first you make a Corrupter, then have it cocoon into a Brood Lord). The little tiny units on the ground (in front of the Hydralisks) are Broodlings.
The Brood Lords are kind of like Guardians from Starcraft 1. They can't attack air units, and they have long range ground attack. However, that ground attack isn't a projectile, rather, it's spitting Broodlings out which then attack (you can control as well). They have a very short life span, and I'm sure this is something that will get patched; they physically block ground to air from getting close to the Brood Lords. If you get enough of them, and your opponent has no Air-to-Air, you win!
It needs to be patched so that someone can move through the Broodlings, or just give them a long range projectile attack. Ground to Air can't do anything to Brood Lords.