[aseipp]

To be technical, it's more that it can read and write the on-disk Git format directly, like many other tools can.

I think the easiest way to conceptualize it is to think of Git and jj as being broken down into three broad "layers": data storage, algorithms, user interface. Jujutsu uses the same data storage format as Git -- but each of them have their own algorithms and user interface built atop that storage.