That was interesting to listen to. As a surfer I used to wear a vest with a hood, even in the summer, when I was wearing a thin shorty wet suit. I was no fashion item but it meant I could surf for 6-7 hours in a day without getting too cold. I even surfed in January UK temps in just that vest and hood, just once. I lasted 40 mins before I got out.
The Point made in the radio broadcast is very relevant here. Once you get out of the cold your capillaries start to open up again and draw warm blood away from your core to the surface of the skin. This leads to secondary cooling and hypothermia can set in really quickly, after you get out of the cold, if you don't do something about it. I used to jog up and down the beach for as long as it took to warm through. Not so simple if you are exhausted.