He will encounter black people all his life. Perhaps his therapist came up with a way to help him cope with an assumed past trauma?
It’s odd you did not notice any strange behavior from him while you interacted in person. She makes it sound as if he had a meltdown after your play date ended.
We’ll never understand some peoples behavior. Having her out of you and your daughters life is a good thing. Unfortunately Alexandre lost a little friend and an opportunity to socialize due to her decision.