It could be the other way around. The person came to HN in a good faith but faced unfair downvoting of otherwise reasonable comments. Which eventually made the person write in their profile what's currently written.
Sometimes people become toxic because they weren't treated fairly.
This thread shouldn't be about how the guy was a meany poo-poo pants, but about what is it with today's world that makes people fall for the most unbelievable things based on the flimsiest of evidence. People with harsh words speaking the truth are far less worrisome than mobs being suckered by obvious falsehoods based on 10 second video clips, a random tweet, or some random post on HN's.
Sometimes people become toxic because they weren't treated fairly.