I don't know what mouse driver I was using (I don't use a touchpad except on laptops, and all my linux machines have been desktops). I would have assumed it was whatever the default was for Ubuntu over the years. :)

(Actually, I do remember that in some versions you had to figure out how to trick the system into thinking you might have a touchpad before it would provide you a place to change the mouse wheel scroll direction, but that seems like a separate failure of preference panels, rather than the root of the issue).