Our player can be embedded onto Facebook directly. When the viewer clicks the 'Share' button on our player for Facebook / Twitter / etc., the player is embedded onto Facebook. Then, we pick up every domain the player tag is embedded on, to display it in your report, so the Facebook domain is picked up as facebook.com.
You can also upload your videos directly into Facebook's CMS, and your videos on Facebook will be played back through Facebook's player. But, since this activity is in Facebook's player, it won't be reflected in our reports.