> If you had included the previous word, it would be blindly obvious that “on a medium“ is only talking about the transport layer, not the format of the data.

I can see your point. But OTOH if providing the "preferred form of the work for making modifications" requires not squashing commits into a big mess to frustrate someone trying to make sense of the code (I'm sure the Google engineers making modifications prefer to look at individual commits!), and Google is using Git anyway to create those commits, then it seems to me like there's an argument to be made that the customary medium used to interchange a range of Git commits is Git.

But the stronger argument is that the Android build system expects everything to be in Git: https://news.ycombinator.com/item?id=49368983