App Authentication is different than App Creator login access into the AppSheet account.
When an AppSheet account is created, a particular individual account is used to establish the login credentials into that account. All billing for apps under that account are then directed to the owner of those login credentials.
Apps, within the App Creator account, can be configured as to WHO can access them - Google Groups being one of those choices. This just simply means that each user, who is a part of that group, can gain access to the app once they have properly authenticated using their normal credentials they would use to log into Google workspace.