Slavery and indigenous are not considered immigration. You might want to study again about this.

Being multiracial, and of indigenous ancestry, does not necessarily mean or always count as immigrant. It is nebulous. No definitive conclusions, in regards to immigration, is made about those of mixed and indigenous ancestry. Speaking of mixed ancestry, the US has a very significant percentage in that category, from both the census and DNA testing.

There are also Canadian and Mexican indigenous people, who refute or argue about immigrant status, regardless of their present citizenship. Making the argument that their people were already in America or pushed out of their lands.

I don't know what pedantic definition you're using, but the context was clearly about indigenous or not. Insisting on a definition from a completely different context doesn't make you right, it makes you annoying.