I'd say there are three likely possibilities: First, that it was an intentional head shot (in which case the shooter was a moron), second, the hunter was looking at those antlers, or, third, the deer was alert and whirled either to get away or to face the sound.
In a related story, when I was a little kid I accidentally made the same shot on my first archery buck. I'd killed a couple of does with a bow, perfect shots, but I just couldn't quit looking at those antlers. I was luckier, though, my old Bear Razorhead greenie did a better job than that Wasp, even off an old Bear Polar II compound set at 40# that I shot fingers w/o sights. What is really amazing is that I made that terrible of a shot from just four yards.
Brannon