Help understanding the peertube P2P system

Can someone help me with how peertube P2P works? I can understand how ActivityPub is used for all the "social" parts but I'm a bit confused about the actual video player.

Redundancy:
I have my own instance and I made a redundancy of a video from the blender instance. if I watch the video on my instance I see 2 peers, my instance and the blender one. I can seen both in Firefox dev tools.
If I watch the same video on the blender instance I see 7 peers, the blender instance, mine, and others. why are these extra peers not showing on my instance? do I need to do something? If I watch the video on one of these other instances mine does show up in the their peers list.

I also made a video from framatube redundant but my instance doesn't appear as a peer on framatube.

Client P2P:
If I watch a video does my browser share It over P2P? if so what is the point of this? it seems to lose the video as soon as I leave the page so this functionality seems a bit useless to me.

EDIT: Answered in comments.

BitTorrent:
If I download a video I get the option of a BitTorrent torrent. If I seed this torrent can it be leeched by web clients? I tried and It doesn't show up in the peer list. What's the point of running a full BitTorrent tracker if it doesn't work with the main P2P system?

EDIT: BitTorrent is incompatible with webtorrent that peertube uses. Peertube also uses HLS instead of webtorrent and behaves a bit different (you can't seed it with a webtorrent client).

Peer discovery:
As I said in 1 and 2 how does the player actually find peers? Is there something like DHT or a tracker built in to peertube? if it's an internal tracker how does the tracker find peers?

EDIT: It uses a tracker build in to peertube.

Thanks for any help.