I guess that's true, so i'll be explicit about that too:
These Google developers are working on Swift because they are part of a team that supports internal-facing IOS tooling.
(there really is nothing down this rabbit hole, FWIW)
One thing to realize, if you don't already, is that we have come to accept that everyone notices everything we do on github at this point (and further, we assume that people look to see what googlers are doing outside the google org as well, and that pretty much everything placed on github will leak, and ...)
If we were trying to keep something major under wraps, this would be an exceptionally bad way of achieving that.
The public docs we have even show that we discourage private github repos for various reasons. Our general internal answer would be "don't stage it on github at all unless you are willing to see it leak"
Seems like the simplest explanation to me.