Bit of a leap there. I'm talking about confessing to murdering someone on reddit for instance cause that is what we are talking about: comments made years ago on reddit. Yeah, sure, maybe someone will tell the cops and they will have to investigate you based on your comment about murdering someone, but then what? Sure, it will have consequences for me, but they cannot convict me based of a single comment and nothing else. How the hell is that going to hold up in any court?
And now think back on what we are actually talking about: comments admitting to having illegally downloaded some content. I would assume they won't even try to start investigating that. Like how on earth are you going to get proof of that?