Also, 7000 feet is not an altitude you would fire at a ground target from. Time will tell if this was pilot error (oops, arming switch was on and accidentally squeezed off a few shots), or aircraft malfunction (fired without input).
I'm not aware of any auto firing systems for the vulcan on an F-16, but it doesn't mean it doesn't exist. Could have also been some kind of mis-identified target and th computer decided to shoot. (I don't think this was it, just giving a lot of possibilities.)
You are right, there are many possibilities as to how this could have happened. 7,000 feet is definately about 6,900 above where these guys would normally strafe from.
It could be that with the Presidential race being portrayed as being so close, that our guard and reserves had began practicing the strategy used in the Clinton era of firing from the stratosphere, anticipating a President Kerry to carry on that liberal democrat tradition.