I think the post is making the point that over the course of human history, low calorie, low sugar diets were the norm. Periods of fasting were the norm.
Many people make that claim, but it isn't backed by science.
Well fasting at times was normal. Everything enough though is questionable. We know that humans have been eating some high carb foods for ages. We also have every reason to believe that humans used to be more active than our "couch potato" current life. There were no office jobs, if you wanted to eat somebody had to chase down the food (sometimes a literal chase, sometimes just find it). Low sugar - there was plenty of fruit available at times. Of course this fruit did have a lot of complex carbs as well.
You touched on the 2nd part of this, exercise. Walking for transportation may seem "radical" today, particularly in the U.S. But this is only radical in a modern context. Walking is our "natural" mode of transportation.
