Actually there are two things that must match:
the torrent's hash
the tracker URL including a valid passkey
When downloading a torrent, it gets the tracker URL with the downloading member's passkey inserted into the information contained in the .torrent file
However, assuming it is a same hash torrent, the tracker URL can be edited, so it contains a passkey. Most torrent clients have functions to edit the tracker URLs, or there are "Torrent Editors", including online. So downloading it is not the "only" way to get the right tracker URL with a valid passkey.