Well, first, every rule has exceptions.Fair play Dachs, you've convinced me. I was under the false impression that there were at least some academics who supported this origin. I still find it very weird that it was named after his first name (and indeed find the strange aesthetic interest in his first name even more weird) but if actual historians don't think it's weird then I'll go along with that...
Also, while the trend about naming places you described is generally true, take into account that, it was pretty damn unlikely for a commoner to get a place named after himself before the Age of Discoveries anyway, be it by first or last name, so this trend really only developed after that particular naming.