There's a definition disconnect happening between Reddit refugees and more experienced Fediverse users. Identical terms seem to have different meanings here:
Reddit: Kbin/Fediverse
Post: Article or Thread
Top-level comment/thread: Post
Comment: Post
Microblog (No real Reddit equivalent, profile posts maybe)
Subreddit: Magazine
Upvote: Boost
Thus, making a new "post" is called creating a new "article", while making a top-level comment (starting a new "thread") or response to that article is making a "post". Any other comment is also called "posting".
It's confusing as heck, but it's natural that a different social media ecosystem would have different terminology.