If any user is not logged in then he will have usergroup, Public and Guest.
As user gets logged in, he will have his own usergroups and Public usergroup. So it means Public usergroup is assined to each user and guest usergroup is assigned to non-logged in users.
Hope it make clear.
It will be great if you can share your view on JED
extensions.joomla.org/extensions/access-...nt-restriction/25829