Yes, time exposed to cold water and how quickly you dry off and get into relative warmth makes all the difference. Those soldiers were just in the water too long. 50 degrees is still too cold for prolonged exposure. My guess is that whoever was in charge figured the air temp made things OK.
The colder the water and the colder it is when you get out the less time you have. When the water is 32 degrees and the air temps even colder, the timeframe is pretty short, especially of the wind is blowing. I think also your general physical condition & health matter too. Having had hypothermia once I can attest that your thinking becomes muddled causing the choices you make to potentially make matters worse. Best to stay dry in winter if you can.