There's a pretty detailed article (http://www.dailymail.co.uk/sciencetech/article-1022822/Incredible-pictures-Earths-uncontacted-tribes-firing-bows-arrows.html

There's a pretty detailed article (http://www.dailymail.co.uk/sciencetech/article-1022822/Incredible-pictures-Earths-uncontacted-tribes-firing-bows-arrows.html http://www.dailymail.co.uk/sciencetech/article-1022822/Incre...) that explains what anthropologists assume they're thinking. It's basically "Stay Away" since the plane is a foreign object. In fact, you can see the tribesmen readying their weapons in case the flying object veers towards them.