It's a little hard to tell from the picture since it's a little blurry, but that looks like a control cable. Can you move/pull the smaller circular 'button' on the end of the cable? What it looks like is a remote trunk release - basically a cable within a cable. Again, it's hard to tell because the picture is blurry, but if it has an adjustable locknut on it (it looks like it does) my guess would be that it's a mechanical control cable.
Can you unscrew the end piece off of it? If it is an antenna cable, my guess would be that it broke off and you can unscrew the end piece that should actually be inside the antenna base assemby.