I seem to remember reading something after the Kim tragedy about hypothermia causing a condition that makes the sufferer feel as if they're overheated.

As mentioned previously, taking off layers to prevent one's self from overheating is another reason, and stress or exercise in any temperature could cause sweat.

I don't know that these are explanations in this case, I'm just relating the idea that there could be any number of reasons for a person to take off clothing in a survival situation.