Let me see if I understand this issue correctly...
You are a lemmy instance admin. If a user from your instance is moderating a community, then any report in that community that is made by a piefed user is also forwarded to you. This happens even if the user being reported is not local to your instance.
You might not know the answer to this since it happens rarely, but does this happen for reports just in local communities, or also in remote communities that your user is a moderator for? So, if modA@slrpnk.net is a mod for commA@notslrpnk.net, do you still see the report if a piefed user makes a report in commA?
I have both a piefed and a lemmy instance I run for testing things, I can try to mess around with the different permutations for this one.