3) Can anyone comment on where this attack comes from?
If the person was wearing armour then wouldn't it equate to grabbing the sode? But then why call the attack katadori?
If the person was wearing a kataginu however, the attack and name would seem plausible.
I Know that Ueshiba, in Budo Renshu use's the term Kata, and Sode. From the picture's it's impossible to tell a difference, other then the Sode in some drawings is a little lower on the arm. In that book techniques 49-60 are Kata and techniques 61-76 are called Sode. Both look to be grabbing the cloth. In Aikido Densho, there are six techniques labeled Kata and three labeled as Sode. Aikido Densho follows almost exactly the same order as Budo Renshu, the only major difference is that there are fewer techniques in this manual. But You can clearly see that Kanemoto Sunadomari was trying to show Ueshiba's techniques.
So I would bet money that Ueshiba himself made the distinction, why he called one Sode and one Kata, I don't know. But 11 Kata, and 15 Sode tell us that he was very interested in that kind of attack.