There are several valid places to draw the line between what is and isn't a social network, but aren't there enough similarities between Reddit and HN to not dr

There are several valid places to draw the line between what is and isn't a social network, but aren't there enough similarities between Reddit and HN to not draw it between the two? Subreddits is the main difference I think, but that sort of thing can't be a requirement because Twitter doesn't have something similar.