what does "unknown" mean?

David Pescovitz, on BoingBoing, has posted an interesting update about the photograph of that "unknown" tribe in the Brazilian jungle, which was remarked upon here. "Unknown" and "uncontacted," it turns out, are not the same thing. Pescovitz cites Survival International's clarification:

"For the avoidance of doubt, let’s just make it clear – yes, the tribe is uncontacted, that is to say, has no peaceful contact with outsiders. But no, they’re not ‘lost’ – they know where they are, and anthropologists, Survival, other NGOs and the Brazilian government have known that there are many isolated Indian tribes living in that region for decades."

This suggests several lines of thought regarding authenticity, indigenous people, and photography, but other obligations preclude expansion upon them here.