A stream of links upvoted by many people. No retweeting happens, which is why you don't see the same link every time someone votes it, only when someone resubmits it (after months or years usually).
Hackernews too has a culture of outrage, at times. Some articles stay on the frontpage for an entire day with very active comment sections. Most of the time outrage (though sometime the joy of a productive discussion).
Mastodon also seems to have less of a problem with retweeting (called boosting in masto), users seem to prefer their own content and boost only a few toots (though also from experience, less active users tend to boost more, me included a few times a week).
I'd report your comment to the moderators but I don't know how.
Let's not have a pronoun flamewar please. Everyone just resist.
The guidelines that say "Please respond to the strongest plausible interpretation of what someone says" and "Don't feed egregious comments by replying" combine to give good guidance here.
While it could be that (I give it a chance of 10%), there's a more likely explanation: the parent just didn't read the post or skimmed through it, so they don't know whether the author "clearly identifies as "he".
They just respond to the headline "retweets are trash" with their opinions on retweets, and used "xir" to play it safe regarding whoever the author might be.
Many people (many have said so in HN discussions) don't read TFA, or don't read the whole FA, and hardly care enough to read bylines and who the author is, etc. They just come straight to the comments, and discuss the topic as a subject they have an opinion about, not based on what TFA says.
I think the user is troll baiting because the author is explicitly identified as "he", not "xir".
This has been established in meta-HN discussions, with many people saying they come straight to the comments.
Even more so, "Alexis" the author's name, even if one bothered to check it, can be both male and female, depending on the country.