[warrenm]

...says the person replying to a comment ;)

[ziggus]

Allowing comments on a news aggregator doesn't mean it's a forum. The fact that HN purposely doesn't have much of the standard functionality of a forum should clue you in to the fact that it isn't one.

[hypertele-Xii]

https://en.wiktionary.org/wiki/forum#Noun

forum, noun: An Internet message board where users can post messages regarding one or more topics of discussion.

HN is clearly a forum.