alt Hacker Newsyes, and per HN terms and conditions only YC and YC affiliated (as you quoted) can use the api legally. I don't license my content to anyone else and so it shouldn't be use by anyone else, even if it's available on a free-for-all API (nice move HN, btw).
https://github.com/HackerNews/API/blob/master/LICENSE
It's right there, you just have to click the link I shared ...