A childhood belief about rude bits

Well this isn't mine, but its my brothers. He's ten and I've been his guardian for two years, I guess I need to pay a little closer attention to him. Last year his teacher gave her email address to the class if they needed help with homework or something I guess. My brother decided at Halloween he'd send her an e-card, well guess what it was. It apparently it had a picture of a vampire and said "I want to suck your clit". Yeah, she called me about it and luckily wasn't really mad, I think concerned was the word she used. Anyway, I actually thought it was kinda funny but had to have a talk with him about it. I asked him if he knew what a clit was. He said yes. God, I thought, I seriously don't want to have this kind of talk with him. I asked him what it was. With all sincerity he said it was the skin on your elbow and pulled on his to show me. I guess some kid at school must have told him that, I didn't ask anymore questions I just told him not to do anything like that again. What makes me wonder more is, why the hell he wants to suck his teachers elbow or even suggest that? He mentioned he sent a card out to Joel, his best friend, too and who knows what that one said.