The Last Updated By field is a reference field for all entities and is related to change tracking. An editor is any user who has made a change to the entity.
To find all entities where the last change was made by a user e.g. Administrator:
LastUpdatedBy = Admininistrator
To find all scripts that have been last updated by members of a group ( e.g. Tester Managers):
EntityType = Script AND LastUpdatedBy = MembersOf('Test Managers')