Just there you screwed up. Telling a 8 years old kid he did something stupid (when actually it wasnt that stupid, he was just trying to be helpful) is never a good idea. I think you should come to him first with apologize. Tell him you shouldnt have said that, that you appreciate him helping and then explain to him why he shouldnt have done that without insulting him. THEN MAYBE you'll get some sort of apologize from him. Just my two cents