I think it's just someone e-mailing anyone for a good prank. Stop talking to him and he'll stop. You're not making it better. He could have just typed out any e-mail adress and it ended up being yours.

Once I had this guy e-mail me asking me what time we were supposed to go to the theme park. I just told him he had the wrong e-mail. Another time I e-mailed somneone and the wrong person got it and he politly told me it was wrong.

Just some examples on how e-mails can get mixed up.