The Linux client will only display history for its own backups; not for any other machines under the same user. You can achieve what you're looking for by using sub-admins and roles. Your account currently has one sub-admin and a custom role, but they aren't being used. Depending on what they were created for, you can re-use them or create new ones.
The first thing you'll need to do is get this user in to its own user group. Then you can create the sub-admin account and activate it. Then create a new role and set it to only apply to the desired user group. You can also select which capabilities you want the role to have or not have, then add the admin to the role.