I think there's two angles to this: general cognitive dissonance, and a sense of power.
There are few things online which engender cognitive dissonance on the level of piracy, which explains all sorts of cringeworthy behavior online dating all the way back to the LOL, LIMEWIRE animation from like 2007. The fact is that piracy is an anti-social act which harms creators, but the convenience of the act (the lack of legal consequences) combined with the personal benefit of saving money means almost everyone does it anyway. And what happens when people who consider themselves good or reasonably moral people are faced with the fact they are regularly committing an immoral, harmful act? Their brain twists over itself to resolve the dissonance. "Ah, actually there is no real harm, you see I never would have bought the thing anyway." "Ah, actually, I would have bought it (I'm a good person), but I just can't afford to right now." "Yeah I'm kind of an asshole, I pirate, but in a lovable edgy way, I'm the cool uncle." Etc. And in a vacuum, the brain's natural self defense mechanism will protect someone from self-reflection or the need to acknowledge personal guilt. But GSwole doesn't allow that to happen and repeatedly confronts people with reality, thereby throwing the false harmony into disarray and forcing one to confront the cognitive dissonance again, which is unpleasant. Nobody likes that.
Secondly is the sense of power. There's almost nothing worse (metaphorically) you can do on the internet than care about something, because caring is weakness. The seminal visual novel Cross Channel (one of my top 5 "everyone should play" visual novels) has a line where someone observes that love is a battle wherein whoever falls in love first loses, because the other person will have all the power over them. Similarly, online, expressing that you care about something opens up an avenue for strangers to have power over you, and this power they WILL notice having. The meaning here is obvious. GSwole doesn't want people to pirate their game. Person B pirates the game. Person B has the power in this dynamic. They feel a sense of dominance and superiority surge through them like pure energy, as ridiculous as that may sound. On a subconscious level (and sometimes conscious) one begins to feel that they are genuinely just better than the other person on some level - they are in some kind of dominant position. And this leads to looking down on them. There is an almost compulsion within people's minds to belittle and mock those one perceives as beneath them. It's a famous theme in fiction for even those trying to repress this to end up belittling in the other direction, where they reveal they look down on others through their efforts to not do just that. It's a very nasty, primal aspect of the human mind.
And so what happens in this thread is that GSwole openly expresses that he cares about piracy, ergo inspiring those in the thread to look down on him, then he confronts them with their cognitive dissonance, giving them impetus to lash out. Consider "cool" h-game devs who are "chill" with pirates. It doesn't really matter if on the inside they are seething too. On the outside if they present themselves as chill, then there is no power imbalance, and pirates dont feel superior to the devs - they aren't encouraged to belittle them. Then if the dev does not thrust dissonance in people's faces, they are content to remain satisfied and content with themselves, no need to go out of their way to prove a point or establish any aspect of their being or be snarky or self-defensive and so on. That is much wiser in every way, so it's what most people do where they can help it. The problem is just that sometimes, a person may care too much to do that.
