No, he's writing in the syntax of Emacs org-mode, which GitHub also recognizes. Parts of it are similar to markdown, but parts are different.
For example, `markdown inline code` vs ~org-mode inline code~, and
```
markdown code blocks
```
vs
#+begin_src
org-mode code blocks
#+end_src
And [markdown links](
https://daringfireball.net/projects/markdown/) vs [[
http://orgmode.org/][org-mode links]].