Where to start. No eye pro is a fail. Mortaring a rifle to clear a stoppage should be done with the STOCK CLOSED! Stopping the drill is a fail. Is there a timeout when someone is shooting at you and your gear chokes? Yelling "stoppage" is pointless. The other shooter likely didn't hear it, and really doesn't care. His only concern now is covering your area, which means yelling "cover" is a far better option and its universally understood by all parties involved. Yelling "cover" indicates that your gun is down, you're down, or both for whatever reason and your area and yourself need someone or several others to cover you and your area. The reason you called cover is a moot point. Other than that, it was rather funny to watch.
TDC