Your confusion is coming from Roles tab in Privilege rule. Basically we don't mention Access Role in privilege, it's just showing the references (showing all the access roles where this privilege is mentioned).
Hope this clears your confusion
Access Role controls all the security for group of users (Access Group) and contains all the privileges.
These privileges can be defined in some rule types e.x. Flow Action. All the users which have that privilege (which have that Access Group) will be able to perform that Flow Action.
Operator maps to Access Group
Access Group contain Access Roles
Each Access Role contains ARO which have privileges