This is a feature provided by Shopify in conjunction with Facebook's Messenger app. When you are going through checkout, at the bottom, you can choose to opt in to receive updates on your order such as tracking information via Facebook Messenger. (You will still get email updates as well.)
This is an app provided by the official Facebook and Shopify websites. This information populates because you are logged into Facebook on your browser, and you may uncheck it. This messaging service only occurs if you have opted in to receive updates during checkout. It does not matter if you have Liked our page or not. If you accidentally opted in, and would like to opt out, you may do so by going to your order page and scrollling down to the bottom to select "TURN OFF".