As long as a site is open for new members, may it be by invitations or open signup, it is possible for them to get an account.

Their personal seems to be around on all four big semi-private gay-torrent sites and numerous other general public or semi-public, see for example there > hXXp://www.pornguardian.com/publicstats.php
That is nothing really new.

IMHO, if they would be after the individual members of the torrent sites via IP tracking, it would be known. Nevertheless, me prefer to use a VPN.

For tracking they provide rather a "Source-Trace Watermarking Service" as they call it. That is a way to track the down the subscription site's member who first shared a movie. With that the site owner has much better information to identify that member: his subscription information (for example a selection of credit card number, e-mail, IP, name and address, date of birth, ID card number for age verification etc …)
See as an example of such technologies > https://forum.gaytorrent.ru/index.php?topic=20023.0