I see 18 posts and 6 unique posters, if I've counted correctly. It's probably easy enough to get 6 of your friends to post for a day. After that is when it gets hard. Skip ahead a month and see what the post volume is like.

I'm curious to know if HN did a "Show HN" else where, or if the traffic organically snowballed.

It's easy if you have access to a big list of users from somewhere else.

I used to run a stack of private torrent trackers. The first one I made came from the fact that the admin of another site ran off with all the funds and abandoned the users. I moved them all to my site. Then every time I set up a new site I had thousands of users I could message to let them know. On the final one I had 100K+ active users - a message to them was like having your own private army to do your bidding for you.

That's what I want to experience in my life.

Look at the next days. It had a gradual start