Genetic testing on ancient Egyptian mummies showed they were most similar to modern day Arabs. Sub-Saharan African genes made up 6-15%, which is much lower than today's Egyptians.
From https://en.wikipedia.org/wiki/Ancient_Egyptian_race_controve...
From https://en.wikipedia.org/wiki/Ancient_Egyptian_race_controve...
Looking at the sources for that wiki article, this appears to be one of the largest and most recent DNA studies on ancient Egyptian remains: https://www.nature.com/articles/ncomms15694.
Edit: To stay on topic, my textbook in a two semester art history survey ("Janson's") said that the defacement of Egyptian statues was due to religious iconoclasm without further specifics. I'm going to accept this as the mainstream academic consensus in the early 21st century. Perhaps unsurprisingly, this matches the general thesis of the parent article.