I just went to the MTG: Salvation forums, and there’s nothing about this there. That’s the biggest Magic website around. I’m calling hoax based on that, plus there are way more cards than just those 7 that could be considered racist.
In fact, the entire game is based on 5 different colors that are pitted against one another. Most of the original cards designed by Richard Garfield were designed to hate on the other colors.
It’s not a hoax: https://magic.wizards.com/en/articles/archive/news/depictions-racism-magic-2020-06-10