Reddit is shorthand for "subreddit or subreddits on this theme".
This place really doesn't look so different to r/programming+r/technology.
I think it's rare to see "Reddit" used to refer specifically to a subreddit. The two words are distinct for a reason, after all.
And I have noticed that there is a 1-3 day lag from the front page of HN to the front page of /r/programming+/r/technology. My guess is most of the frequent contributors there see the content here on HN then repost it.
Reddit caters to, essentially, everyone, by allowing users to create separate topic groups, while HN is a single collective forum for tech-y/science-y/thing-of-general-interest-y type news.