For a lot of mailing lists, one unsubscribes by sending an email with the word "unsubscribe" to an address formed by adding "-request" to the end of the name part of the mailing list address. It's very easy to slip up and send that email to the mailing list itself. So this person was _trying_ to unsubscribe, and by now has probably done so, but that explains the weird one-word email.

People come and go from mailing lists all the time; we all have only so much time and energy to pursue all of our interests. I seriously doubt it has anything to do with your mail to the list (except perhaps in the incidental sense of reminding him he was still subscribed).