These are markdown files served from ~hidduc-posmeg's own planet and converted to HTML by urbit, proxied by ~hidduc-posmeg's star ~doznec. Since this system isn't actually supposed to be live yet, hidduc-posmeg.urbit.org is DNSed to doznec.urbit.org; ~doznec talks to ~hidduc-posmeg over Urbit's own network, an encrypted P2P protocol (%ames). Ideally, hidduc-posmeg.urbit.org would DNS to the actual Unix server the planet is running on, for obvious reasons.
This whole thing, like http://www.urbit.org, would fall over in a few seconds of HN traffic if it wasn't behind an nginx cache. However, if you look at your network window you should see a long-poll. If ~hidduc-posmeg edits zir tutorials from vim on zir Unix server and saves, this will drive an update event that'll propagate forward and refresh your browser. You can see this in action in our demos...