Do you know what an observational study is? Nothing was manipulated. There were no variables against you. The site's actions were observed. It's absolutely no different than someone seeing how attendance changes at the local park in different weather. You weren't part of an experiment like Facebook was, where they changed stories that came in to elicit emotional responses.
I'm assuming you're talking about this post, which was an "experiment" done by a normal user counting the amounts of shares on posts. It was only statistics gathering. How would you opt-out of something like that?
I will attempt to mentally exclude you next time I observe something about Hubski, if that helps. That's all I can promise. However, if I make a mental note to the tune of, "Wow, there's a lot of people commenting on this article!" and you have commented, I cannot promise you will not be involved in that observation.
Then you probably shouldn't be posting on the internet. Hubski didn't perform any studies on you. You're just paranoid. You might want to smash your TV while you're at it, pretty sure there's an NSA camera in it.