I don’t doubt the authenticity of this at all. My uncle was a missionary in Papua New Guinea in 1975 - actually from the early 70’s until the late 80’s. He has told me about similar people groups.
We were there in 1976 and briefly were in the back country in the mountains. Everyone was excited and happy to see us, especially if we would shake their hands, because we brought cash to buy their objects and because for them, white is the color of death and we were thought to be reincarnations of their dead relatives.
The one exception was a village selling walking sticks and masks. Only the elder males were selling and there was no “#2” price. These guys were surly. One of the tourists, a Canadian woman, tried to bargain them down and they just refused. My husband had been watching one of the men and detected that he was simply aggravated by the woman. So, on the way out, my husband offered this guy a price above the Canadian’s, but still, a tad below the asking price. To everyone’s amazement, the seller agreed and sold us 2 wonderful masks and 2 terrific walking sticks. DH says to this day that it was a guy thing, they connected on a shared male level and the seller was just showing his contempt for the Canadian woman.
I wonder if, at some point, members of this tribe who are now deceased _had_ encountered white people, but that it had now become myth. These specific individuals may have never seen whites before with their own eyes. There were a lot of missions and also Australian doctors and other government workers, even in the back country, but I can believe there were remote villages even further away that just never got more than 10 miles from their homes.