If the press was saying there were no shots from the hotel, yet the tankers say they were taking significant fire, then someone is either incorrect or is shading the truth.
Now, I'll take your statement and try analyze it. Some people in that building said they didn't see any sniper. That probably is very true. If this guy pulled out a gun, fired, then quickly moved, they may have never seen the man. This is not a big surprise that they didn't see the gunman.
Now, as for the military, they were under fire. Somebody in that tank or nearby spotted a sniper. This was either from the eye or from a sensor that picked up that flash/heat/or infra-red on that scope. They had every right to fire back. This is without a doubt.
But, this is not the reason Shep made the statement.
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.