Sure, but when you're walking all the time, none of that time is wasted, because you're helping your body and brain function better. When you use a car, you really are wasting all your transportation time. To get the same benefits, you would have to drive places, and then go walking recreationally after, which would clearly take much more time to get the same utility.

Their next sentence shows they traded one form of exercise for another. That's "surreal"? There are many forms of exercise.