He definitely is using Emacs for most of it. He authors his posts in org files, and uses ox-hugo to export to Hugo.

I do something similar for my blog, except Pelican is my backend.

https://andreyor.st/posts/2022-10-16-my-blogging-setup-with-...

Interesting. I think I must've seen the same post when he posted it. Nowadays I just use Pandoc to go from markdown (with extras) to html.