All users, visitors, guests, members are getting emails if those are subscribed. And there is an unsubscribe link in Email content. So all can be unsubscribed using the link in email content. Also all logged in users can unsubscribe using the link on comment form as well.
Please try to use different users and emails to see those. It seems you’re only testing using admin and you’ve even not checked subscribe checkboxes on comment forms and you’re not subscribed at all. The email you’re getting is the default WP Post author email. It’s not wpDiscuz notification about new comments.
Also please note, there will not be any email notification about new comments or reply if the new commenter is the same person. You see your comment so there is not any reason to notify you about that.