> That quote doesn't quite explain the difference between writing and typing. Both use your hands after all.

True. Although the article is about writing on paper. I'm a pretty good touch typist and years of Vim have made me efficient with the keyboard. My typing is much faster than my writing. I'd say that even if I am thinking deeply about a subject, if I'm copying the text via typing, it I'll be a lot faster than writing. On the other hand writing gives me the opportunity to slow down. Maybe you're right that both should work equally if I'm invested mentally in the material, but then I'll have the internal pressure to type faster which might hurt that. As a physical motion typing is rather static when compared to writing, so I do believe an actual difference exists.