I don't buy the "explnation" of the redditor, the post came across more like a contrived explanation that sounds right to non-IT people. EVERY place I have worked it, including smaller places had some sort of out of band network to connect to hardware on the IP network in the event something happened. I find the credibility highly dubious to be quite honest. For example, a financial place I worked for, every single network engineer had access to the routers/switches in the data center. If FB has segregation where network engineers require a sysadmin to unlock the access to hardware, there is something more going on to require that level of security. Getting past the man trap, pin keypad, and retina scan is one thing, it's not like you haven't been logged 3 times in 3 places getting into the data center, requiring a baby sitter to access routers is a whole different level of paranoid.

Also before anyone says the BGP messed up the DNS that is why the doors/security didn't work. What happened to the the interior network DNS, you are going to tell me they didn't architect the external and internal separately?

I suspect in reality this was an announcement to FB and others. Keep eyes open.