This is mostly crap advice. Human body has evolved for physical activity. Healthy amount of muscle is strongly correlated with longevity and high quality of life. Hunter-gatherers have naturally muscular physiques and they have a lot of "exercise" naturally.
Discussion
Do you know what didn't have the hunters-gatheters?
Long lives.
That article is nonsense.
"For hunter-gatherer communities, we need a different mathematical model because, without healthcare, infant mortality rates could be in the region of 20-40%."
Hunter-gatherer communities dont have specialisation, thus can't have science and modern healthcare.
You can not change the model in order to not taking into account healthcare so that you can be picky with the numbers.
If you are talking about live longevity, you have to count infant mortality.