That’s interesting. Since I type far quicker than I can speak, I would have definitely expected typing to be quicker than signing.
Its depth is quite fascinating -- ASL truly is its own language, not just "English with your fingers". (Though I should add I don't know it myself, this is just based on discussion with an interpreter friend.)
Are you sure about that? People hold (enthusiastic) conversations at 160 WPM, and the the fastest typists in the world average around 180 WPM.
Now that I think more about it, maybe the raw speed is not quicker, but the quantity of ideas conveyed per unit of time is higher due to being able to scroll back and forth in text for the listener, as opposed to wasting time clarifying mumblings or repeating what one said. Especially in a group setting where you do not have to take turns speaking.