@ln it's not always a Lemmy thing.
Recently I noticed that a lot of my posts with certain tags, were ending up on Lemmy. After some investigation, I found out the community they were posted to, was hosted on fedia.io, a Mbin instance.
So, either Mbin or specifically fedia.io is creating posts there based on certain hashtags used across Fedi. My Fediverse tagged posts have all ended up there recently, completely unintentional on my part.