You know how someone blowing in your ear makes more sound than when you blow in someone else's ear? The airflow itself can make sound from eddies and whatnot.

Most people don't put their ear next to a case fan to see if it's annoying or not. You experience its sound from several feet away, and the measurement should reflect that.

I think they mean the excess noise of a volume of air moving past your ear, which is due to the turbulence created while air is passing over your ear and not the soundwaves being transmitted by said volume of air.

Practically speaking no you wouldn't want to factor the turbulence generated at the microphone because the user of the computer wouldn't be hearing that.