I think you missed what my point was. They are all family.
Most such experiments carried out in 'the west' are done with strangers. This is a non-trivial difference.
Go to the Ozark mountains in Arkansas and find a small cluster of cabins in the hills where the inhabitants are all family and rarely venture away. Offer the uncle and his nephew the same deal, suddenly the same 'anomaly' will show.
The thrust of the article is not "this one tribe is an anomaly in how we think and judge", but rather "it turns out that the biggest anomaly is the people in the USA". Up until now the model formed from looking at 'Westerners' has been assumed to be 'the norm' or even how we are physically wired, and unchangeable. Any observed deviations from the model are anomalies and interesting. The novelty here is that actually, things may be the other way around.