As someone who identifies as being both Black and Latino, I sometimes get that side-eye response.
It can be difficult for a lot of people to understand ethnicity and race are two different things. In the most basic of basics -- ethnicity has something to with our cultural identity. Race is a way of identifying people through physical traits or characteristics. We should also take into consideration that the media’s portrayal of cultures around the world can leave certain people out -- so people assume people of certain communities all wear the same skin.
Black people do not have one culture -- we can be islanders, Latino, Indian, Chinese, or Australian. Black people inhabit every inch of the world, and we practice different religions, speak different languages, dance different dances, eat different foods, have different perspectives.
I think when we look at ourselves and our culture, and think about how different it can be from the person who shares our skin color across the world, we get that “a-ha!” moment and realize, culture isn't necessarily dictated by the color of our skin, or vice-versa.