Public GitHub repos are viewable by anyone with or without an account. You can view and clone the repo if you know the correct URL.
Private GitHub repos are only accessible to those given access.
Within the scope of this terminology, my understanding is that this repo is private. I think I'm right based on https://news.ycombinator.com/item?id=13682657 and https://news.ycombinator.com/item?id=13682501. Am I right?
Within the scope of corporate security, I understand that the code is being moved out of the local intranet onto a non-corporate-managed Web service. However, GitHub manage private repos for some fairly high-level groups (or at least I assume they do), so their data protection policies are clearly very decent. (I at least know that individual floors on the building are keycarded, which is nice. I learned this from a story posted here by a guy who got fired.) So, even though this is an impressive level of stupid, I'm relieved that no leaking can/will happen (particularly for your sake now you've posted this here).
OP, please note that several people have reached out to you from top-level comments. If you could add a new comment listing an email address (IANAL but a new gmail one would probably be okay), or even better yet put it in your profile, that would probably result in some nice leads for you.