Choosing the All Sites in the filter drop down does not show Private Sites that a user is a member of.
Steps to recreate:
Add some Public and Private Sites and make a user a member of these Sites
As the user change the drop down to All Sites.
It will show any Public Sites regardless of whether the user is a member of the Site or not and also shows a "View All" link with the number of Sites that the user can browse. The number of Sites reflects the total number of Public Sites and Private Sites that the user is a member of but when you click View All the pop-up once again only shows Public Sites.