I think it is a load of rubbish.
A lot of people spend prolonged time outside at 18C and are fine.
I can have my house at 15C, it's about 18C at the moment and although it doesn't feel warm I certainly don't need the heating on.
Part of the reason for that is that I keep the humidity under control. Although there are some other factors like using clothing and ability to tolerate cold which differ from person to person.
Houses with high humidity feel a lot worse at a similar cold temperature than ones with low humidity. In my opinion anyway.
The key to good climate control in my opinion is understanding the relationship between how warm you feel, temperature and humidity.
And to do it efficiently in terms of cost you need to consider what is the real issue that is causing you to feel cold. Lowering the humidity for example may result in you feeling warmer at much lower cost than just turning the heating on to maximum.
Unfortunately many people in the UK believe that the only solution to cold weather is to fire up the boiler. But climate control has moved on from that.