He's clear that's it's mostly writing, in this section:

https://paulstamatiou.com/made-on-an-ipad-pro/#how-i-use-it

It does wander quite a bit (such as the section on maintaining a static-site blog), but I was fascinated because the topics were generally things I have experience with.

To answer your question, Paul made much of his work for the past several months on his iPad Pro, including the blog post that we are reading.

This is a great opener which makes me not want to trust anything this person says, "I have never been into tablets. I’ve had numerous ones over the years from iPads and iPad Minis to Androi..."

Yeah I did a search for "Surface" to see if he even compares the two devices and nothing, something tells me this might be a narrow view of the work-tablet world.

It’s a reference to the old apple campaigns around “made on a Mac” and “made by Macintosh” decades ago. I touch on it the last section of the post.

perhaps the website and post was made on the iPad? /shrug