Black people have the same problem from white men and women for the same reason, a sense of illusionary superiority and the need to prove it via control of someone they consider less than. I have met and seen white men like that and even black men that try to emulate the white patriarchy to feel secure in their manhood.
I wish the girl would have said to him, “Thank you for your advice! I don’t need to convince you if you want cookies, you may need to figure that out for yourself or just leave rather than reduce yourself to being a rude harassing male with a superiority tone. I am a kid and you need to be show example by being more respectful, especially for your age.” I know in most “customer-is-always-right western cultures, she may be ridiculed or fired for standing up to the bully, but I know a few places where she and black people as well, can stand up for their rights against this type of tripe.
As a boss, I am sure you support your girls and let them know why he behaved like a rude Neanderthal and how to deal with them in a way that keeps her safe and keeps her confidence and integrity intact. She will meet more like him and need the tools to deal with them.
Thanks for sharing.