So no, your assumption is completely incorrect. Even if someone shoved a passthepopcorn torrent in there, (a) that person would likely get banned from ptp, (b) it probably wouldn't work in the first place because joker's servers couldn't join the swarm and (c) the information that the owner of joker can glean from such a torrent file would be almost entirely useless unless the goal is boosting the ratio of the user.
As much as you'd assume about something you've never used, private torrents are actually a well-oiled, quite secure machine. It's easy to think of pirates as incompetent, but Gazelle is actually decent software and the biggest problem I ever faced while involved in that scene was DDoS attacks against the trackers.
