Partly! The tools they mentioned (IDE, Mercurial) don't impact the app itself though. Which makes them irrelevant and doesn't factor into why their codebase is massive.
They are relevant if you take them for what they are: examples that explains, in a general way, why FB has large codebase. Because when something doesn't fits their needs they will write their own version.
So I guess with iOS they wrote/rewrote some part of the system functionnalities to better fit their needs.