I think you are confused:
In the activity report the link is just a link to the url that generated this action , but if you click on it you just see that page but logged in as admin, so you get a certificate with your name, not the user name, this is the way it is supposed to work, this is not a bug.
Read Dale's response and mine, they give the only ways with the existing code to get certificate for a given user.
If that doesn't fit your need, as you say you will have to write some code, but I suggest you don't try to modify the activity report without understanding what you do because if not, you will most likely break things