So, this meme.
tl;dr Mastodon users occasionally spam mentions and Lemmy (and probably Piefed) ingests them all and makes the post across all of the mentioned communities.
Sucks, right, because on the theadiverse, you’re not actually able to do that so easily.
Basically, it’s because Mastodon mixes mentions with addressing. Every mentioned person gets addressed, even though sometimes you don’t mean for it to go into that community.
So what if Lemmy, Piefed, Mbin, and NodeBB made it so that only the first matching community gets the post? We can already tell which posts come from threadiverse software and which don’t (because we use audience, Mastodon doesn’t.)
Just an idea, I can’t speak for the other softwares.
Just tested it. A Lemmy-Post is only created in one community, even if other communities are mentioned.
An external post (in this case from WordPress with the Activity Pub plugin) is only posted into the Lemmy community that is mentioned first.