There are a lot of factors at play here. 

I mean, objectively speaking, she is correct. "Race" doesn't exist outside of social / cultural context. 

However, socially and culturally, some might argue she's erasing much of her heritage. Though Western/White culture does that already by referring to anyone from Africa as African instead of by their country. Hell, Western culture does that to anyone with dark skin and broad noses regardless of where they're from. I mean, we don't do it with Europe. As already stated, we're Irish-Americans or German-American. Never European-American. American culture is full of faults in its racial system. But, it's already so ingrained into our every day life that we seem to think it's almost a necessity. Not to even mention "mixed" people who probably have some of the worst of it when it comes to identity. 

I don't really have a solid opinion here. All that I know is that our racial system has so many flaws and discussing what a celebrity chooses or chooses not to identify as is just pulling a small twig off a very large and very old tree.