That's only the DSM-IV definition. Psychology is a lot bigger than that, and the English language is bigger still. The difference between passive aggression and aggression boils down to whether the anger is being expressed directly or indirectly. It isn't solely determined by inaction, and there's a spectrum in-between the extremes. Letting air out of someone's tires is passive aggressive because it avoids confrontation while causing harm, whereas going up to the driver and punching them in the face is aggressive and does not avoid confrontation.
Faking niceness is similarly passive aggressive because it avoids confrontation while causing harm. Adding sarcasm into the mix, admittedly, makes it more aggressive, but it's still more passive aggressive than being straightforwardly aggressive in the first place.
Regardless of whether or not I'm right, regardless of whether your comment was disingenuous, passive aggressive, aggressive, or sarcastic, I'm unhappy that you're openly and unapologetically being uncivil on Hacker News, it's against the guidelines, and I'd like it to stop.