Show HN is for things someone has made that other people can try and this is a write up which is perfectly fine as it is - https://news.ycombinator.com/showhn.html
I'm not sure what you mean by that. Most reading material is just fine as a regular post and can't be a Show HN, thats very near the top of the thing I linked:
On topic: things people can run on their computers or hold in their hands. For hardware, you can post a video or detailed article. For books, a sample chapter is ok.
Off topic: blog posts, sign-up pages, newsletters, lists, and other reading material. Those can't be tried out, so can't be Show HNs. Make a regular submission instead.
Things that can't be Show HN can be perfectly fine regular HN posts, just like this thing already is.
I'm completely confused here, sorry. Are you talking about this submission? People submitting their own work with their first post is totally fine, especially if they're around to talk about it. These are some of the best threads HN has to offer, often. The guideline is about not using HN to post your own stuff exclusively but it's, you know, a guideline rather than a mathematical constraint so the trivial case of posting your own stuff on HN for the first time is not merely fine, it's a good thing.
Edit: Maybe I'm figuring it out, is it that you thought that self-posting is strongly discouraged and that 'Show HN' is a label you're supposed to use to identify self-posting? They're not directly related, Show HN is just a special HN category with its own subsection and its own extra rules. Nobody has to use it but if you do use it, the post has to be within those rules. The other, somewhat orthogonal thing is that you can post your own stuff (in or outside Show HN), just don't overdo it.