Just because `jj` wraps around git doesn't mean it cannot have another backend. My comment doesn't imply that it only wraps around `git`. More importantly, the other backend which `jj` offers is (afaik) exclusively used at Google. Unless you are a Googler you will be using `jj` with `git`.
Also, the comment was aimed at a person who is obviously very invested in `git`. I was doing my best to offer them a description of `jj` they could swallow.