the temprature of the atmosphere at a high altitude is around 500 . yet an animal would freeze to death and not boil . explain

Every body in this world radiate heat. The temperature of a body remains constant if the heat radiated is equal to heat absorbed.
The temperature of atmosphere is high but animal freezes to death rather boil , this because of the fact that heat radiated is very less thann heat absorbed.
How is this happening?
The density of atmosphere is very very low , i.e., the number of particles in atmosphere is very low and thus number of particles interacting with the body of an animal will also be very low.Hence the heat which animals radiate is greater than heat absorbed even though the tmeperature of surrounding is very high. This is the reason for freezing to death, low density of atmosphere even though the temperature is very high.