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Peripheral vaso-constriction acts in everyone to conserve heat by shutting off blood flow to the extremities. As a cold water distance swimmer who lives in Northern Europe, this still happens me in temperatures I consider very warm (18C). I feel cold to the touch while remaining completely comfortable. Most people however do not undergo any adaptation training. Therefore after swimming recently around Manhattan island, the adapted cold water swimmer had problems with the heat, while the untrained swimmers were picking up thermal blankets afterwards. (Which I found fucking hilarious).
The adaptation process is actually a combination of habituation and acclimatization, i.e. first getting used to cold shock, then being able to extend the exposure duration. There is a difference in being used to certain ambient temperatures,as you mention, and actual cold adaptation.
The latent heat in a body can’t be instantly bled off in a short period of time. While unconsciousness or more likely extreme lethargy, may result in people from warm climes, that will actually result in slowed heat loss. There’s a saying in hypothermia, (which I’ve to various degrees maybe a hundred times, very rough quick guess) “you are not dead until you are warm and dead”.