It looks like they might be using a loophole since their product is training for jobs they are using that as a substitute for, “we’re hiring.”
They claim that they do not charge you anything. So, how can they scam you? Of course, besides your hours and the potential outcome (code). Just curious.
The proper way to deal with such issues is to email the mods at hn@ycombinator.com.
This is in the HN guidelines: "Please don't post on HN to ask or tell us something. Send it to hn@ycombinator.com."
<https://news.ycombinator.com/newsguidelines.html>
The post yours linked to appears to have been removed, so the immediate problem has been resolved.
(Not a mod, just an active participant.)