I'd say that was racialism. It's one thing to intern individuals born abroad or even the first generation born stateside. They were interning individuals with 1/16 Japanese blood, which is to say they were interning the great-great-grandchildren of the original Japanese settler stateside.
In the memoir I remember best, by a woman interned as a little girl in Idaho, there weren't any great-greats. She described a lot of grandparents and parents who were born in Japan, and kids who were born stateside, mostly in California. A lot of the old men and many of the young men talked about fighting for the Empire of Japan, because America was vulnerable and undisciplined.