This seems like a common misconception. The mention of the staging area in the README points to https://martinvonz.github.io/jj/latest/git-comparison/#the-i.... I'm guessing you didn't click that link. I suppose we need to inline part of the text where we link to it to reduce the number of confused readers.

At this point, I wonder if maybe we should not even mention the staging area. It seems to confuse a lot of people, so maybe it hurts more than it helps to mention it.