It’s a shock that in this day and age, where one can easily fly across the globe in a few hours, that there is still a tribe of people living in the jungle who have yet to be contact by the civilized world. Well, “uncontacted” doesn’t really mean what you expect it to mean. According to this Q&A, uncontacted pretty much just means they are not friendly with the civilized world. They could be well aware of the “outside world” and may even have some technology, but they just want no part of it. So pretty much they are a bunch of city slickers who retreated to the jungle, and after a few centuries in isolation… poof, an “uncontacted” tribe.