It wasn't like back on Earth, where racism was based on nationality, cultural difference, skin colour, social hierarchy, or caste. It was much simpler, where a certain group of normal humans thought that they were superior to variant humans, which stemmed back from the Ancient Ages and is prevalent even today.
I wouldn't say that most people in this world were against variant humans since it was mostly only men who had such a mindset, and you'd very rarely see a girl who had the same thoughts. But if you were to ask a normal human guy if he would prefer a variant human girl to a normal girl, then I'll just say that there's a higher chance that he would say no.
I thought Nina would say something in return when she heard the racial remark about her since she seemed like someone who was proud about the heritage she was born into and seemed like a strong woman who would never let another's comments get to her.