I think Chris has got it. The fins have not finished extending yet. Judging from the size of the missile, the date it was taken and the platform its launching from, it makes sense. On the TOW, the forward fins flick out forward and the rear fins flick out to the rear. Plus, they are offset slightly, which accounts for the apparent difference in size.
If you look at the position that the fins would be in when fully extended, it makes total sense. They were probably testing the lightweight TOW launchers that eventually ended up on the Cobra. That'd account for the lack of Huey TOW launcher visible in the pic.
I'd call this one case closed!
Jon