Yeah it would make them a racist. Because its most likely hate or disgust for the other race which is causing a person to be against interracial marriage. But for same sex marriage, there are BS religious reasons to be against it, not just hatred or disgust of gays.
The "BS" in "BS religious reasons" is the tell. There are huge swaths of the Bible the religious set is happy to set aside when it's convenient. Go read Leviticus for a start.
It says more about Christians than it does about gay people or even the Bible that they're fixated on homosexuality.
