The "hairdrier" was probably a joke or slang, as in a "heatgun is a big hairdrier". "Фен" doesn't mean "regular fan", it's "hairdrier", despite sounding very similar.
I did learn that фен can actually mean other kinds of hair dryer-like heat guns (from https://ru.m.wikipedia.org/wiki/Фен). I assume that’s what these folks used to heat various components.