I distinctly remember the day our then 5 year old boy/girl twins were telling us about someone they had been playing with, using the child’s name. When we asked who that person was, they both described her as “the one with the brown face.” For them, skin color has always been a descriptive term, no different than hair or eye color.
For the boy in this story NOT to be inquisitive about why someone has a different skin color seems more worrisome than that he did ask.
You are 100% right. Children’s curosity is innocent, its the adults in charge that are nuts and see racist in another when they should be looking in the mirror for racism.