[s0rce]

I also thought the same thing. The article didn't really address the point specifically, if you are highly active most of the day you will burn a substantial amount of calories. Some people maintain weight while consuming 4000+ calories per day, for example on long hiking trips or long distance running.

I'm not sure about the hunter gatherer example. That was interesting. Maybe they are in much better shape and can be active a large portion of the day without expending much more energy. Or simply, the activity isn't extremely high-level.