The torrent client works successfully without announcer and behind NAT. How?

Question

bittorrent

I was given a torrent file with no meta information (no list of trackers/announce URLs). I am behind NAT. At the same time, I successfully find distributors, upload and distribute the data myself. Up to this point, I was sure that the tracker is required + it is necessary to forward ports for incoming connections. In this regard
1) How do distributors find each other without a tracker? (Nothing comes to mind.)
2) How is distribution behind NAT without forwarded ports? (UDP Hole Punching comes to mind, but that again requires an external server, which isn't there.)