The network is the computer
From the article:
The other big question is how a "server configuration change" led to not just Facebook but also its Messenger, WhatsApp, and Instagram services going down. That would strongly suggest that Facebook has either connected them up or attempted to connect them up at a low level, merging them into one broad platform.
While it's always nice to spread fear and paranoia like this, there is a rather obvious answer which does not involve such exciting scariness: it's pretty likely (and also well-known to actually be the case) that Facebook, along with other large organisations, don't send their backhaul traffic over the public internet. Instead they have a lot of physical connectivity that they've bought or leased, and they send traffic over that network. And, obviously, they send all their backhaul traffic over that network: Facebook's traffic, WhatsApp's traffic & everything, because why wouldn't they do that? If that network gets fucked up, then everything that uses it falls apart, and this outage has all the characteristics of some internal network outage: someone made some configuration change to a bunch of switches or routers and everything fell apart catastrophically, we've all been there, right?
Sharing a common network infrastructure is not 'merging [distinct services] into one broad platform' any more than the fact that my web browser and NFS client share the same network in my house is 'merging them into one broad platform': they're just sharing some infrastructure.