Most likely, it is included in some kind of ThirdPartyNotices.txt that ships with the game. It's actually pretty hard to sneak third party F/OSS under the radar in the company of this size - there's automated code scanners, among other things, and while they can't catch everything, they sure can flag a copy of a public project on GitHub.
I'm pretty sure that declaring https://github.com/s-macke/FSHistory/tree/master/data to be MIT-licensed does not actually make it so... (these are disk images of the relevant FS releases, which are still under copyright as well as provided under a proprietary MIT-incompatible license)
TL;DR: A Microsoft contractor basically endorsed piracy, in a weirdly-recursive-enough-to-be-legal way...