A subscriber on the mailing list has clicked the unsubscribe link in an email thread you're quoted in, but they have used your unsubscribe link instead of their own. This generates a confirmation email which you have received. We will monitor the situation to determine if we need to remove the unsubscribe option which allows people to do this, though we added this link after there was a large number of people posting 'unsubscribe' emails to the list.

It's working as intended. As long as Lu doesn't click the link or reply to the email he won't be unsubscribed. It is similar to someone sending a password reset by clicking your account name on social media. Annoying at worst, but not much to care about. imho. -- /ahnberg