It's the same thing honestly. Facebook has a boatload of projects that have nothing to do with Web. They probably spend more on their ML stuff than any other department in terms of infrastructure / resources.
At one point I ran across the statistic that said that Facebook's internal network had more IP addresses than the entire public Internet. Maybe whoever claimed that exaggerated, but all the Web stuff Facebook has to offer doesn't need even a single percent of IP addresses of the entire Internet.
Also, as far as I know, Facebook has its own h/w ambitions. It builds its own h/w and equips its own datacenters with it. While this is definitely not their main business, h/w development is a lot more resource-intensive than s/w development when it comes to datcenter usage (when it's about developing datacenter h/w).
