It's technically a bit more than that. JJ is its own VCS, with pluggable backends. Google has a closed-source Piper backend, the git backend is the only real open source backend. But at high level, it's fine to think about it in that way, yeah. I tend to think about it as being more "able to work on git repos" than as a UI.

I can't hear Piper backend without thinking about Pied Piper

Not the only project that's working on that.

https://www.gameoftrees.org/