Okay, so with those settings none of your users should be counted as Private.
Question: Have you changed the privacy settings since your App was first published? That is, is it possible that the Access was initially set as Private, and later changed to Public?
User quotas are team based rather than project based. On a Starter Plan you’d be limited to 10 private users in total across all projects.
What do you see on your Usage Dashboard?
The only thing I can think of at this stage is that you might have had users sign into one of your projects when it was set as private, and the usage count hasn’t reset yet.
If you have the emails of users that might have signed into any Apps as private users, you can try purging them via Settings → Data → Delete User Data.