I agree that it sounds like Niggas.
I think I might possibly have read the word once or twic myself but i am not even completely sure. How is a ten year old supposed to have heard about it?
Who here was familiar with that word?

These "spelling bees" must be something uniquely American. I really don't think they exist this side of the Atlantic. I don't quite see the point in them, although I suppose anyone who aces them is bound to do well in the English "SAT" in the future.