Looks like it's his no-URL-included submission that worked.
In theory, there might be a minimum karma to post URLS. The official HN FAQ only notes a minimum karma to be able to downvote. There are unofficial FAQ's, but I pay too little attention to be able to recommend one.
You can see a lot more if you toggle the “showdead” flag in your profile. A lot of posts go into the “dead” state right away, usually because somebody keeps posting nothing but links to the same blog. I see he had one “dead” back in 2017. My advice is he should:
1. Look at articles on the front page, pick out a site which frequently gets articles there
2. Look at 10 or so articles from those sites and pick the one you like the best.
But the subdomain matches your user name and your account does not have a history of engagement with HN (irrespective of its age). That may correlate with low quality content in general and threrefore there might be a "self-promotion" heuristic in place.
It's not that self-promotion is banned on HN. But using HN only for self-promotion is generally discouraged (or explicitly discouraged) because it sucks up oxygen without much benefit to the community.
In theory, there might be a minimum karma to post URLS. The official HN FAQ only notes a minimum karma to be able to downvote. There are unofficial FAQ's, but I pay too little attention to be able to recommend one.