When you say the user was able to view the report, do you mean he was able to view the report under the reports list in the navigation bar? or were you referring to data/rows within the report? RLS would only work on the rows (data), reports would still be viewable. If you want to hide the reports, then you'll have to categorise them into different workspaces or groups.
And, users mark as admins can see all data within a report regardless of the role, in other words, admin previliges override your role.
Thanks
Kaz