No idea what Plume is, but I may Google it once I post this.
Threads is Metas (Facebook parent company) attempt to grab a share of the Twitter market share as Elon does his best to decimate his company.
If I understand correctly, Threads uses the same/similar publication method as Lemmy or kbin or Mastodon so the data can be freely shared between them all. So in that sense, you could argue that Threads was just a Mastodon instance being run by a company that has shown little regard for its users, and far more regard for its profits.
Note: this is a very, over simplified view of the landscape that isn’t technically correct however is an attempt to convey a picture that helps put the pieces together in a somewhat relatable way.