Selection effect. You also didn't see anyone with cleft palettes or appendicitis or iodine deficiency. If somebody gets sick or injured in that tribe, they're much more likely to die than in most places. Also, sick or injured people don't romp around the forest checking out strange birds in the sky.
Yeah but compare the groups you saw there to some random groups you'd see in a mall here. There's a pretty big difference.
They have been there for quite a while, and humans are great at adaptation.
If we couldn't be reasonably healthy at such conditions, humanity would have been extinct long ago.