Suppose that the aunt was a lesbian that married a woman instead of a white man. Does that mean the entire family came to America on some gay shit?
Also, look at Liberian history. There's a good chance that their family has a similar lineage to yours.
That said, I feel you about immigrants who don't like African Americans. I've had black folks from Africa or the Caribbean come up to me and talk shit about Black Americans that would make Uncle Ruckus blush. They assume that because I'm white I'm going to cosign, which I don't!
As much as I avoid these folks though, I wonder if a lot of these attitudes are based on an ignorance of how America works. In many diaspora countries the majority of black people are immigrants. In others the colonizers left as soon as they couldn't own people anymore. In America it's the complete opposite and that creates a very different dynamic to what exists in other countries.