An honest wish to understand the word as it is probably the best way to have adequate cognitive reaction in order to survive.
You seem to recognize this, by referring to it as being used "tongue in cheek."
So, to be clear:
You are offended that the author used an offensive phrase in an ironic manner clearly meant to both vindicate the targeted minority and point out the failings of the people that would use that offensive phrase in earnest?
In short, you're now upset by the form of the communication, rather than any of its actual content or meaning.
Another commenter suggested that you are partaking in some cargo culting of your own. I think they're onto something.
This is much less clearly tongue-in-cheek, and even if the tone is meant to be generally humorous, that wouldn't exclude it from being actually offensive.
Cargo-Cult behavior truly is everywhere!
What makes you so sure they are talking about New Guinea island with the term stupid savages?
Cargo-culting happened in all of Melanesia. I can't see any reference to cargo cults in west of New Guinea island. A few mentions of it in PNG, etc.