I was trying to give simple explanation for someone who said they don't know networking.

BGP in this context implicitly meant external BGP . Yes, no single router necessarily sees all the routes, but all routers combined generally see the internet as a single network of networks was my point.

Convergence in this context is how most ASN will resolve on where/how to route a specific ASN traffic.

It is hard to peer with someone and not trust the routing table they publish, that is why Pakistan could by mistake block YouTube for everyone few years back.

In this case if you peered with Facebook, and they published incorrect routing for their AS you would accept it.

This doesn't mean FB couldn't have used multiple ASNs did some rolling updates etc, however without knowing what exactly fb screwed up for five hours it is hard to say what they could done differently.