Yes, that's correct. Another reason was that Mercurial is easier to customize because it's written in Python so we could sometimes just replace whatever we needed without needing much changes from Mercurial itself.
Yet another reason is that the .git directory is considered a documented API and several other tools and libraries depend on it (e.g. JGit and libgit2). So any new features for Google would need to be made to those tools too if we wanted things built on them to work.
Yet another reason is that the .git directory is considered a documented API and several other tools and libraries depend on it (e.g. JGit and libgit2). So any new features for Google would need to be made to those tools too if we wanted things built on them to work.
We also consider Mercurial to have better UX.