I don't see another reading, but perhaps people are misunderstanding you to mean that you don't believe the Native Americans. Perhaps if you suggested an alternative title?
I imagine it's getting downvotes from people who tire of the tendancy of a chunk of the HN commentariat to dismiss anything as "not a real problem" if it doesn't impinge of straight white guys, and have assumed your response is a thinly-veiled version of that.
That's an odd phrasing for something that should be very easy to verify.