Social media typically implies a website where users are sharing self-created content. If a website with comments counts a social media, than all web2.0 is social media and there's practically no distinction between the web and social media.
A blog that has a comments section is primarily still a blog, it just has a secondary social media feature attached.
In the case of HN, most people are here for the comments section and frequently don't even read the article, so it's primarily a social media site with a news aggregator feature.
Social media typically implies a website where users are sharing self-created content. If a website with comments counts a social media, than all web2.0 is social media and there's practically no distinction between the web and social media.