Microsoft actually hand over OS code to states regularly for certain contracts so I figure they don't need to protect most of thier code like that.
I think this makes more sense for a secret project (e.x. the next iPhone), but honestly as a security person it seems overkill for anything outside national security responsible code, like state sponsored malware.
I also find it strange that the code is apparently somehow accessible outside that building (see the fired comment). If this was anything beyond security theatre, it'd be on an airgapped network and that wouldn't even be a concern (as the employee wouldn't be able to access the code from their laptop). Seems excessive for very little gain.