Pretty much, yeah, except it can utilize Debrid services, Usenet, I2P, etc. as well, not just bittorrent. The base app itself can't actually pirate anything on its own; you use plug-ins to facilitate that ability. (Without any plug-ins, the only thing it can do is list movies/shows and where to purchase them from, which is how its able to be listed in app stores.)

And yes, when paired with Debrid, it basically works llke PopcornTime. One person downloads the torrent, then it's stored on a server where anyone using the same service can stream it instantly without having to wait for seeds. It's really simple and convenient, much easier than downloading the torrents yourself then sticking them onto Jellyfin. Just open the app, pick something to watch, and watch it.