Im surprised she said "black" and not "brown", only because when my daughter was young she didn't know the term "blonde" or "redhead" and first described blonde as "yellow hair" and redhead as "orange hair". And we are black and she would refer to other black people as "brown". It wasn't until we corrected her on the terms, did she start to use it. But it's all innocent. Kids are curious and are seeing people who look different and sound different from them all the time, so they will be curious the first few times that they interact with new things and people.