I mean I don't think anybody said it was?

OP said real feel was -21, which is an accuweather measurement used to determine how the temperature will feel and affect an individual, taking in to account other factors as well as temperature (https://www.accuweather.com/en/weather-news/what-is-the-accuweather-realfeel-temperature/156655).

Another example of where real feel can be used is how on a very humid day in summer it can feel a lot hotter than it actually is.