Census Bureau update says 2.4 million Indians

Part of the recent 10% growth per year of Native Americans in the United States, my two little ones. Their tribe? The Nava-Sioux-Mohawkian-Seneca-Tuscarora-Cayuga one. At Indianz.com the article Census Bureau update provides look at Indian Country caught my eye. It says there are 2.4 million Indian people counted. 4.2 million if you count mixed-race Native Americans, although, why are we (I am 13/16th's American Indian) counted separately? Or are you only counted separately if you mark two boxes? Being 3/16th's European ancestry mean...