Why would you think a random person on HN is less prone to talking out of their ass than a random person in the CS/engineering/VC world? Than a random person selected from the population of the world?
Or let me put it in plain English: an HN reader is more likely to have a Chinese/Indian friend/colleague on H1B, and if they ever discussed anything outside work, chances are that these topics come up, and they get exposed to more information in the area. If you are actually interested in immigration topics, you'd probably learn a few facts there. At least between people on visa, these topics get discussed all the time.
I understand that not everyone is based in US, they may not be in such a situation, or their conversations never reach these topics. But I would think they'd shut up instead of giving their opinions. That's called basic courtesy.