The most important lesson to learn from this successful "launch" is that they iterated on their product for seven months of beta before officially launching it. How often do you see "Show HN's" of half-finished side projects with no actual customers? All the time. And the feedback is rarely good. Even if it is, the percent of qualified leads will likely be drastically lower than if you release a refined product, sinc…
The way Show HN has evolved over the years, the bar for it is naturally low. Show HN is for something you've made that other people can try out and talk with you about in the thread. That can be anything from a first project or weekend hack to a feedback-honed product like you've described above. The only rules are (a) you made it and (b) it works.
By "it works" I mean that it isn't a landing page or an email signup or a fundraiser, but rather something other people can play with and give feedback and ask questions about. That definitely includes new products, but also other things. Who knows what people might come up with! It just has to be interesting.
A risk with setting the bar too high is that some users will feel like contributing isn't for them. We want to avoid that. There are many talented people who maybe haven't done anything of their own yet, or haven't yet shared what they've done, or who suffer from that curse of our field, impostor syndrome. It's painfully easy to look at the polished work of others and think, "I could never do that". One reason we want Show HN to be welcoming to all levels of work is so there will be plenty of examples where people think, "I could do that". Not as in "meh, that's nothing," but in the DIY spirit of "hey, me too".
But the main reason is that many kinds of things—including seemingly trivial things—can be interesting. There's a secret relationship between the high and the low. They thrive together.
Masterful paintings are wonderful but first sketches are interesting too, especially in a workshop or a studio, which is the kind of place we want HN to be. Besides, first sketches have a way of turning into something masterful later. Most won't, but some will, and we love it when HN helps that happen.