When creating a custom meta class and linking it to e.g. a customer object, the meta class and it's data is shown on the customer object.
With AddPermissions() access rights for this metaclass are added for the "administrators" group. Non administrators, that can see/edit the customer object, also have access to the tab for the metaclass.

It would be great if the access for the custom metaclass rights were implemented on the tabview level

It is also a limitation at API level as well, accoring to support, so the API should be enabled code to customize the tab level permission as well