Moodle in English

Fabian,

The the most common use of user to user context assignment is the Parent or Mentor role explained here: https://docs.moodle.org/38/en/Parent_role. That's a typical way to set one up. What differs in such roles is the specific capabilities they have; the method of assigning a user to user role will always be the same.

To find out what is happening on your site:

First, the place where a user is a assigned to another user is on the user profile of target user in the Preferences > Roles > Assign roles relative to this user. So take a look on the profile of the instructor user in your situation to see what other role and person(s) has been assigned to them there.

Secondly, this can only happen if you have defined a custom role (or messed with a standard role) so that it is able to be be assigned in the User context. Check in Site admin > Users > Permissions > Define roles and see if any of the roles there are able to be assigned in a user context. You will find that information on the definition page for every role in the "Context types where this role may be assigned" setting where the User checkbox is checked.

Randy