WordPress separates the display of comments from the solicitation of new comments: have_comments vs. comments_open. The
have_comments function looks for a comments count; the Facebook plugin for WordPress loads this comments count from Facebook servers based on the current state of comment submissions and admin approvals (if comments moderated). If you have comments to display then the Comments Box will be rendered by default to display those comments and, in the process, solicit new comments.
If you have no comments count you should see an empty
div#comments, matching the behavior of Twenty Thirteen, Twenty Twelve, etc.
If you would like more control over listing existing comments when comments are not open without using the Facebook Comments Box social plugin take a look at the
style value of the arguments array passed through the
facebook_wp_list_comments filter and return an empty string for the
The string "Leave a Reply" does not exist in the Facebook plugin for WordPress. The Facebook Comments Box social plugin is added to the page by overriding comments_template; check your theme code for a header declared outside of its comments template.