You're immune system lowers when you get cold. So does stress/shock. As the article linked to shows, the more bundled up you are, the less you are at risk.
Likewise, if you start to feel run down and look after yourself, it will just pass quickly.
All that, doesn't seem as relevant, in today's heated houses, cars, buses.
But back even in the 70's, when I was a child, it was relevant. We woke up with ice on the inside of the windows, obe room was heated and the kitchen was warm, if cooking was going on. If you went out with wet hair, it would stay wet all day, shops wasn't heated like they are now. We'd have to wear coats in class, sometimes.
There was still malnutrition knocking about among the WC.
Children died because of their general environment, they developed all sorts of things that they wouldn't have got, if they were MC, or better fed/more warm.
We know a bit more now, but you've got to consider the time and experiences of the older generations, as to why they think the things they do.