menu_class is indeed what changes the ul classe, what's happening there is you didn't set which menu to use here: wp-admin/nav-menus.php?action=locations - which is why it's changing the div instead of the ul.

Once you set it, it'll change the ul. Try it.

menu_class is indeed what changes the ul class. What's happening there is you didn't set which menu to use:

• wp-admin/nav-menus.php?action=locations