Maybe they erased the post by accident? How do you know that your answer solved their issue or was relevant? You might think that was the case but it might not be.
In general, I think this is a extremely silly.
I had instances where I would post about cloud infrastructure and somebody would crawl out of their hole to 'educate' me on colocation, thinking they are solving a ground breaking issue.
Someone is gently, politely, pointing out that the line "welcome to the Internet" is going to cause you problems and your response is to bicker?
There is absolutely nothing serious about the first line. The rest of the post clearly indicates it.
Reminds me of people who will show up to threads featuring proof of concept implementations and comment on how the code lacks unit testing.
Sorry, human beings do not work that way. If you have anything worth saying, you can say it nicely.
Maybe you shouldn't have included that line, then. The comment would not have suffered in any way from being shorter.
I think in many senses, HN is a first generation response to how to get a bunch of people who don't really know each other to have a decent conversation in a low context environment.
But that shouldn't be an excuse for any of us to refrain from providing feedback, insight, and advice online. In fact, we should continue to do so with the understanding that our time in producing that comment/content is volunteered.
And of course, on the other side, we should strive to retain the record of the communication chain if we are the original posters. Deleting a comment is your choice, but it's probably good practice and behavior not to.
While you might think your advice is 'good', other people might not. Nobody will thank you for bad advice.
There are way too many factors when it comes to communication on the internet.
Not everything falls under 'he did not thank me BECAUSE he is a jerk'.
Etc.