So windchill is better interpreted as you will lose body heat as if it were this temperature without wind, but the actual temperature is still the same?
Pretty much. You lose body heat at a rate that depends on the temperature, air pressure, wind, humidity, and maybe more, for example the thermal emissivity of the objects around you (and of yourself).
If you set air pressure and humidity to "standard" values, and wind to zero, you can express the combination of other values as if they were a temperature, and call that windchill.
Of all the variables wind is most important, since the rest don't vary very much on earth. But air pressure does vary on Mars, and thermal emissivity varies in space.
