When restricted users try to access a public projet they are not member of they are getting a mail like

Dear project administrator,

Restricted User (login: restricted_user) requests access to the resource XXX from the project "XXX":
XXX

Restricted User wrote a message for you:
>test

This project is private, only project members can access it.
If you decide to accept the request, please take the appropriate actions to grant access and communicate that information to the requester..
Otherwise, please inform the requester (XXX) that he will not get access to the requested data.

Please note that adding Restricted User as project member might not be enough if you set specific permissions on the requested resource.
--
Restricted User.

The bold sentence is wrong as the project is not private