This isn't preschool where you present your work to the teacher to receive a gold star. This is someone presenting something to "professionals" providing critical feedback. That's always going to be ripe for someone getting their feelings hurt.
Sometimes, it's well deserved feedback that is not pleasant to hear, but if you get bent out of shape as a developer because of it, then you're just going to have a tough life. No developer is perfect. There is always room for improvement. If you think you're perfect and your Show HN is flawless, then please wait while I grab some popcorn.
For this specific example, it's data inadequate type of release. I would say the landing page needs more information, but it's just one page, so the "top portion" definitely needs some work. Great, there's an acceptable display of the various color "charts" that the product actually is intended, but there's no information on what it is, why it works, or why "internet lovers" would be interested.
For instance, the name. I had to internet search to find the meaning of the name to see if maybe that would provide some insight. Nope. That didn't help much at all. Although, I now know a new Japanese word.
This is something that looks to be developed by someone that is passionate about this, but overlooked that not everyone that would view their post as intimately versed in the topic. Let's face it, most devs might as well be colorblind when it comes to the results of their UIs. You can always tell when the devs/coders built the UI vs when a team with actual design skills were involved. Just look at the beginnings of pretty much every single *nix.