Those are the two possibilities, yep.
Two further points of information: I've heard from a number of different people who were watching/listening to a BagCam feed at the time that they heard nearby small arms fire before the tank fired. Further, the Iraqi Ministry of Information could be exerting a strong influence on the remaining journalists in the hotel -- who have all been heavily exposed to Baghdad Bob's reality distortion field anyway.
Given that, I'm more inclined to believe the tankers.