Indeed, they could be compelled to do that, but according to the article they were keeping logs in this case, despite explicitly advertising that they didn't.
Regarding illegle activities, if there is a will strong enough that warrents Powers that be to track down something, one way or another, it will happen. No matter, how much one deludes himself into a sense of security. The idiot in the article shoudln't have been posting shit in a fucking irc channel to begin with.
Pardon my english, am very tired and not my mother-language.