The word "Indian" continued to be used to instill that Native Americans were outsiders and foreign, for which white people were the true Americans. It is a slur, but one generally accepted.
It is curious how "Indian" remains acceptable to most, while some howl that "redskin" is bigotry - as the people furious about "redskin" still call African-Americans "black" and it entirely ok to refer to "white people." But "red people" and "yellow people" is bigotry.
You try to figure out the PC rules of the moment.