New to WordPress. If this problem is due to some WordPress convention, then adjust the rating accordingly.
It's not obvious to me now to disable the footer menus entirely.
From browsing the widget admin and creating blank "Text" widgets, it seems that these footer widgets are Sidebar 1 and Sidebar 2, and that they default to displaying the categories, meta, etc.
Assigning blank Text widgets makes the default content disappear, but the boxes are still visible. Removing the blank Text widgets causes the default content to reappear.
IMHO, when nothing is configured to show in the sidebars, then nothing should show -- they should be empty and invisible. They should not default to display some unrequested content.