No, if you look in the footer you'll see it says "Public file shared from Slack", which I think just means someone posted this document using Slack

Weird, so Slack effectively has a stealth Medium competitor now?

Slack's blog is at slack.engineering. It's called Several People Are Coding. This is not from Slack, as noted by philfreo.

yes this what I was curious about as well. Interesting the simplicity of creating snippets with markdown makes it easy to use for posts as well sharing code snippets ala gists