You can’t do normal BitTorrent in browsers, there’s no support for plain sockets that you’d need to communicate with other peers, WebTorrent is technically a new protocol that implements the BT semantics over stuff the browsers do provide (So you can proxy between the different swarms, that’s the “hybrid” nodes in the image on the WebTorrent page)

But it turns out it’s all a moot point, since PeerTube removed WebTorrent support anyway in favour of their own P2P system

Edit: Ok so I misunderstood, and it seems like it’s a bit complicated. The server can (it’s disabled by default) use WebTorrent to import videos, the client still uses the WT trackers to find peers but uses a different protocol to actually share the video data.

There’s this tool that provides the ability to automatically seed videos, but development has stalled because no up to date client will ever make use of it.

I think the one remaining use is the “download as torrent” option, but even then that’s just using a web seed, so it’s just an alternative way to download the video.