Who can report? is a feature in BuddyPress Moderation Tools that allows you to restrict reporting content according to options. Please, follow Moderation->Settings->General Settings and scroll down to Who can report.
Here is a screenshot showing the Who can report options.
Only Site Members:- If you enable this option, it allows you to limit that only site members can report the content.
Visitors & Site members:- If you enable this option, it allows visitors and site members both to report the content
Demo for Limiting who can report BuddyPress content.