They claim they can track 20% of the public torrents people download, and I suspect it's a very specific 20% corresponding to certain trackers and certain torrent clients. I wonder what they are.
There's no way for any torrent client to hide itself since all this site needs to do is to have a program join the swarm of all torrents it can find and log all the ip's of the peers in that swarm, it doesn't matter what torrent client you use.
However if it's a closed tracker and they do not have access they can't join the swarm and log the ip's. I'd assume that at this point they are only logging ip's on open trackers but there's no technical reason why they couldn't join a private tracker (unless they don't accept more users) and log ip's there aswell.
Private trackers are a lot more difficult. I bet it would raise some eyebrows if a user on a private tracker were to suddenly announce all torrents. On public trackers they can just use multiple IPs, on DHT they are trackers themselves and don't even need to ask others, but on private trackers their crawler will have a hard time getting many accounts to hide its activity.
As long as the connections are direct. If even a small part of Torrent users would use something like OneSwarm, it would provide enough plausible deniability to make this data automatically useless.
