I would argue that it isn’t a calculation, but rather a mathematical description of how quickly heat is dissipated from an object.
I would also argue that an “internal heat source” is a varable in the equation used to calculate the chill factor that the news warns us about, but in an automobile with the engine not running the value of that variable is simply zero. In short, a specfic mass generating X btus of heat per hour will dissipate heat in a Y mph wind at a rate of Z. With X being a lower value, Z will be higher. Etc.
Humans generate heat at a known rate. Therefore, the ambient temperature and rate of wind can be readily factored in to determine how quickly heat will be dissipated and thus, what eth equivalent ambient temperature dissipation rate would be without wind…which gives you the chill factor.
But in truth I think we’re all arguing semantics. Simply, wind has an effect on how quickly an engine reaches ambient temperature. But only if it’s passing over the engine. That’s why we always tried to park heading away from the wind in North Dakota. It helps.