In the PADI Rescue Diver manual that I have, on page 50, there are listed six "signs and behaviors" that may indicate that a diver has a problem. Removing gear, including mask, is the fourth indicator mentioned, not even the first.
To jump to the conclusion that a diver is in distress based solely on MOF is ridiculous. The instructor in this case was maybe showing off to his students, demonstrating his lack of knowledge about the real signs of a distressed diver, fluffing up his ego by being authoritarian, whatever. His behavior was asinine, IMO. I know that in the classes I assist as a DM we discourage MOF because it might lead to loss of the mask. We mention that MOF may be a distress sign if accompanied by other stress indicators.
To jump to the conclusion that a diver is in distress based solely on MOF is ridiculous. The instructor in this case was maybe showing off to his students, demonstrating his lack of knowledge about the real signs of a distressed diver, fluffing up his ego by being authoritarian, whatever. His behavior was asinine, IMO. I know that in the classes I assist as a DM we discourage MOF because it might lead to loss of the mask. We mention that MOF may be a distress sign if accompanied by other stress indicators.