It was my impression that the AC130 video was of an AC130 "Spooky" or "Spectre" gunship. This aircraft will have a number of serious weapons on board. I've read that they carry several Mini-guns, 30mm gatlin gun and the auto loading 105mm howitzer.
So the artillery hits you were seeing could have been from the AC130, if so equipped.
No, those are actual artillery shots coming in. You can hear the gunner at the station yelling out at each shot and then there's a long delay until they hit.