Of course the 6yo was impertinent, she's a 6yo.
She doesn't understand genetics or the captialist system, which my son at 5 (sort of) does, but the average 6yo doesn't.
Given this child's ignorance of race, it implies she has parents who don't put much emphasis on it. Hard to see that as very bad.
She isn't afraid to ask questions which is a very good thing, and if showing early signs of explicit resolution in her thought processes. All good stuff.
My son (at 5) does this sort of thing all the time. At 4 for some reason in the middle of Tescos suddenly called out loudly to us "Why are some people black ?" We were a little taken aback, but he was not being "bad", since to him it's much the same as why cheese is yellow.
So he now knows, though I rather suspect he thinks DNA is shaped like little books :)
He engages the staff at shops in all sorts of slightly surreal conversations about his views on cheese, what he's doing today and why they are wearing those clothes.
He's very popular in our local Waitrose, mostly I
suspect because he's very polite, usually starting with "excuse me".
We don't teach our kids only to speak when spoken to, and certainly do not tell him not to speak to people serving us. Learning the social conventions is part of education, and the more supervised practise they get the better.
We have mentioned that some people do not like their appearance commented upon. It's too early to expect it to work. The standard "what if someone said that to you ?" doesn't work since in his mind you'd either be wrong which he'd argue vigorously as a reflex, or correct in which case he'd launch into a long explanation of it.
His best friend is another colour, but also sadly suffers from a striking skin disorder and a gammy leg. 2.0 didn't care, nor did his classmates until older people started making a fuss.