The user Activity Feed report is helpful to see impersonation information as well as "Initiated by" details.
The "Initiated by" column will show an admin's name if that admin:
Created an automatic enrollment rule that captured this learner
Manually enrolled the learner into the course
To determine which situation it is, someone needs to navigate to a different report that includes an "Enrollment Method" column (such as Course Enrollments or User Enrollments).
Adding "Enrollment Method" to the Activity Feed report would complement the other information already included and prevent the necessity to jump between reports for the full picture.