@polotek reports aren't identifiable, for obvious reasons. They never include the name of the user that reported it.
Also, the post that was reported has to be engaging with your instance in some way, I thought. Maybe they tagged you in the post? Then the reporting user can choose to send the report to all instances involved in receiving the post.
More than likely they didn't specifically choose to send it to you, they just chose to report it to "all involved parties".