Okay, I've set up 'Setting Up' as a category where we can call post stuff like this, that has to do with getting the site up, running, and, um, reasonable.
Among the reasonable things I just uncovered is that admin can change the category of a post in the editing dialogue, by ticking on/off the desired category, in the same way you select a category when posting. Cool.
Among the unreasonable … I think that first post 'Categories' was shown under my name, until I moved it to 'Setting Up'. Then it showed as being posted by deviousdiva. Hmm. Who am I? Do I need ego work? I checked my profile and diva doesn't show there. So where did the author confusion come from?