It's not going to be quite so haphazard as picking it up "wherever". They'll be taught the most important parts, and will absorb most of the detail either by being explictly taught or by repetition and observation. Note that you can't compare knowing to keep your head covered with a piece of cloth or how much water to carry, to throwing an effective kick. They aren't the same kind of learning, at all.They pick it up usually. From where ever. That is hence my point on "formal" instruction, you would be looked at weirdly in some cases if you did a survival course and live in the bush. Yet a lot of people who live in it probbly dont know half of whats in a formal course and do fine most of the time and in day to day living.
Hell some people move to a remote location and literally learn everything through trial and error. They have no prior education or experience in the subject or not enough to make a diffrence in the context.