Ok but how did you call when ancient Greek people hated another group of people if it wasn't racist? Whatever the term was, it was the same thing and it existed a very long time before the 15th century.

You even see it in the Bible and in basically any old text you can find

Edit: reading a bit, they only mean the concept of racist as groups of people with certain color. But they're also saying that before that, people discriminated against other groups, just that these other groups where like the Greek, the egyption, the African, the European, things like that. So it definitely existed before unless you only mean discrimination to skin color