I got what he meant. It was a complex reply with many parts and it seems like it would be harder to dictate or type without having that feedback loop of being able to see what you're doing.
Close your eyes and try to produce a complex sentence in your head. It's not that hard, it's easy to imagine being able to do it with a little practice. Especially if you have a screen reader, or play it back with text-to-speech. I'm sure the poster is clever and impressive in lots of ways, but a blind person writing well does not surprise me.
I already would find it taxing to write a well structured and complex answer like the original comment. I would need to go back and forth, edit, change the order of sentences and the like.
And I am perfectly capable of doing this with my eyes.
But: I would never assume anything about the experience, challenges and abilities of the OP. I was fascinated by the depth of the recommendations and was reminded that I very much need to work on making my sites more accessible.
But I would personally probably refrain from asking if they couldn't just keep a paragraph of text in memory. But that is just me.