When the Enrolled courses option is selected in the "frontpageloggedin" option, users who are not enrolled in any courses can also see available courses displayed on the front page.

Steps to replicate -

1. Go to Front page settings
2. Change all 'frontpage' options to 'None'
3. Change 'frontpageloggedin' to 'Enrolled Courses' and the rest to 'None'.
4. Create a course - do not enroll any users
5. Create a new user
6. Log in as the new user, you will see the 'Available courses' appear on the front page.