The guy has cleary some sort of deformation going on.
He's clearly agressive, being hunted down and flamethrowed.
He has no helmet (not even outside in front of the hangar in the behind the scene shot) where in every shot of the person burning him do have one.
As for the guy who is getting his helmet burned, his skin is not just burning, his neck his morphing and changing color...
Yeah it could be anything but in a movie that deals with bioengineering, with humans discovering vials with probably dna material, mutation do seem to be highly plausible.
Again i dont think this is the main threat (well could be if such thing reaches Earth this is clearly our end) probably one of the many f**k ups that happens when the humans play god (they steal the fire of the gods, the urns, play and shit happens) and i'm sure that REAL creatures will appear.