It's no surprise that when white people get mad the first card they pull is "go back to your country!" But I cannot blame them more, for this ignorant comment, than I can blame a dog who pisses inside that was never housebroken.
American education fails to refer to whites as Europeans just as they refer to browns as Africans. Our education system failing to emphasize that Europeans (whites) are just as much a foreigner to this land as is Africans (blacks).
I'll take it even farther than that; the American education system has tried to buffer out the fact that Whites are foreign to this land by substituting the word European with the word Caucasian.
ex:
African-American: Descendants from Africa
European-American: Descendants of Europe
Caucasian-American: Descendants of Christopher Columbus