In 1978 I witnessed a man on the waterboard for no less than 5 minutes.
At least 45 seconds for each covering of the face.
At the end he was unconscious and had to be tended by the Doc. He returned later in the day but was quite timid and hyperventilating.
Id say what you witnessed was going overboard on the part of the instructors. Might have even called for some disciplinary action. But times were different back then. Real POWs who had returned from Korea or Vietnam were training newbies on the realities they would face if captured by certain elements that had no respect or intent to follow rules of war or Geneva conventions. Even back then, waterboarding would have been mild compared to real torture.