Racism, jokes, or ignorance?

Every Tuesday is an after school English class on the other side of town.
Since there aren't so many Koreans living in my neighborhood, we chose English as his home language, and he gets extra schooling for his home language.

We went to this school, and while I was waiting for his 45 minute class to end, I decided to play in the playground with the other two kids. It was after school hours with a teacher's aid there. In Sweden, the kids can stay after school if the parent's work. They can stay until 5pm with adult supervision.

When we got there, a small kid (maybe 7) starts yelling out "ching chong." After repeating it a few times, I was infuriated, and asked him if he was talking to me. I told him that I was speaking English to my children, but he didn't care, and continued his name calling for 30 minutes. The teacher's aid just ignored the situation. In the end I told the boy that it was not nice to say "ching chong." Of course he didn't care. The teacher's aid tried to explain (after 30 mins of name calling!) that I wasn't chinese, and I spoke English.

Does it even matter that I wasn't Chinese? It is still rude and ignorant.

Finally when the boy understood I was speaking English. He starting yelling quotes from Achmed the terrorist. "I kill you" I guess that is what Americans say???