I doubt it, they had an XMPP interface, but that doesn't mean they use XMPP in the backend
Yeah, I was pretty sure that Facebook was just using straight-up XMPP at one point in time. They have been actively trying to drive traffic to their Facebook Messenger app - first by shutting down their XMPP interface, then blocking applications that talk to their web interface, and finally by removing Facebook Messenger functionality from their mobile website.