XPrivacy - explanation of restriction settings
According to the README file of XPrivacy that can be found here:

The tri-state check box works this way:
unchecked = no items in the category are restricted
solid square =
some items in the category are restricted
check mark = all items in
the category are restricted
Note: By default, categories and functions
are filtered by permission, so you may not see all of them. The check
box state is independent of this.