This has to be a joke, right?
I recognize that the above para sort of sounds like I think I have some authority to mediate between them, which is not true and not what I think. I'm just replying to this side conversation about how to be polite in public, just giving my take.
The broad pattern here is that there are norms around how and when you use someone's name when addressing them, and when you deviate from those norms, it signals that something is weird, and then the reader has to guess what is the second most likely meaning of the rest of the sentence, because the weird name use means that the most likely meaning is not appropriate.
The commenter above doesn't mean that any reference to someone else by name ("Sam Altman was fired") is patronizing.
1) The comments are meant to be read by all, not just the author. If you want to email the author directly and start the message with a greeting containing their name ("hi jrockway!"), or even just their name, that's pretty normal.
2) You don't actually know the person's first name. In this case, it's pretty obvious, since the user in question goes by what looks like <firstname><lastname>. But who knows if that's actually their name. Plenty of people name their accounts after fictional people. It would be weird to everyone if your HN comment to darthvader was "Darth, I don't think you understand how corporate law departments work." Darth is not reading the comment. (OK, actually I would find that hilarious to read.)
3) Starting a sentence with someone's name and a long pause (which the written comma heavily implies) sounds like a parent scolding a child. You rarely see this form outside of a lecture, and the original comment in question is a lecture. You add the person's name to the beginning of the comment to be extra patronizing. I know that's what was going on and the person who was being replied to knows that's what was going on. The person who used that language denies that they were trying to be patronizing, but frankly, I don't believe it. Maybe they didn't mean to consciously do it, but they typed the extra word at the beginning of the sentence for some reason. What was that reason? If to soften the lecture, why not soften it even more by simply not clicking reply? It just doesn't add up.
4) It's Simply Not Done. Open any random HN discussion, and 99.99% of the time, nobody is starting replies with someone's name and a comma. It's not just HN; the same convention applies on Reddit. When you use style that deviates from the norm, you're sending a message, and it's going to have a jarring effect on the reader. Doubly jarring if you're the person they're naming.
TL;DR: Don't start your replies with the name of the person you're replying to. If you're talking with someone in person, sure, throw their name in there. That's totally normal. In writing? Less normal.