Assuming the incident really happened, and there is at least some reason to be skeptical, it’s not the child’s behavior that’s being discussed. It was the child’s aunt that pushed the issue. If she hadn’t butted in there would have been no drama. The OP’s over the top reaction was to her, not the child. The child just got a ‘stern’ look.
According to some random page on “findalink.net?” That’s a real authoritative source.
Besides, there is no one single proper “etiquette.” It varies by situation.