Edit (8-4-2010 13:15):After a more careful viewing of the video involved (I'd only given it a cursory glance at first) I'd be inclined to agree with Banner that they in fact were armed, look around the 3:38 mark in the short version and it definitely looks like one guy is carrying an assault rifle and the other one is carrying an RPG.
This of course does not make the 'insurgent armed with an anti-freedom grenade' any less funny, just that the shooting in all likelihood was justified.