From the actual bill:

63C Age-restricted social media platform (1) For the purposes of this Act, age-restricted social media platform means: (a) an electronic service that satisfies the following conditions: (i) the sole purpose, or a significant purpose, of the service is to enable online social interaction between 2 or more end-users; (ii) the service allows end-users to link to, or interact with, some or all of the other end-users; (iii) the service allows end-users to post material on the service;

I would say that HN is covered under that.

https://parlinfo.aph.gov.au/parlInfo/download/legislation/bi...

You are quite shortsighted if you can't see the possible outcomes of such a far-reaching and anti-democratic law.