Also IP addresses can be spoofed, an extreme example was a teacher who's life was ruined because it was discovered he was stashing kiddy porn on the school issued computer, and then was exonerated because evidence was found that revealed that the actual pedo was using the victim's laptop address as basically a VPN to find this stuff without being tracked.

It appears they aren't taking legal action against the pirates but instead wanting to use them as witnesses against the ISP who has more money to go after and from the sound of it didn't have decent repeat infringer policies in place. They also are after more than just the IP address, such as name, email address, and logs. That would presumably be enough to identify someone more clearly.