1) Cancer has a multitude of causes, some genetic, some evironmental, plenty beyond our control. It is impossible that any group of people is free of it. Cancer starts with DNA damage and as long as humans have DNA, they will be suceptible to cancer.
mrex already poiunted you out to some info on that.
2) Do we even know what are the death causes of a secluded group of people that refuses to get medical attention? Can they identify and diagnose illnesses? Do they have a record of them? I don't know.
I would think it's very hard to know what's going on in those communities without someone else keeping a constant record, so how can you conduct a full scale study without this info?
3) The article only points out external manageable cancer-inducers like smoking. While all this is a point to them, it's not an exclusive feature. Any person can do all the same things and not everyone will be free of cancer, although they can reduce their chances.
I don't smoke and my family has a proclivity for stomach cancer. I live in a place with heavy summer radiation. Care to wage my odds? I am not free of it.
4) Low cancer incidence, in the abscence of external factors, implies a genome probably not carrying many mutations asociated with cancer. For that "healthy" DNA to remain dominant and persisting in time, there must be a rather restricted genetic flow into those populations, which can only mean one thing: inbreeding.
That, I don't have to tell anyone, packs it's own problems.
http://www.ncbi.nlm.nih.gov/pubmed/10332616
http://www.ncbi.nlm.nih.gov/pubmed/23243086
So, there's no secret here to learn. Each community has it's health problems to deal with.
I will however accept their advice on low scale farming and agriculture, in which they seem to excel.