Here's where I think Chris is coming from.
I assume many have read
this story by Terry Dobson? Or read a similar account in Ellis Amdur's
Dueling with Osensei? In both cases, I would say the old man (in Dobson's story) and Amdur (in his story) demonstrated aikido, even though neither performed a technique, or even used the threat of a technique. The distinction I would make between those stories, and the stories of Roman and David is that in Dobson's and Amdur's stories, the "practioner"
engages the threat. Not in a fight, or in physical contact, but on a human, emotional level. And through that engagement, they bring the conflict to resolution.
Had Roman turned the tables on his opponents by good-naturedly joking with them, making friends with them, and possibly even getting his headphones back, I for one would call it an exemplary example of aikido. I'm not saying he should have done that, mind you. In this case, walking away may indeed have been the best option. But knowing "when to walk away, and know when to run" is not just a trait of all martial arts traditional and modern, it's even in a Kenny Rogers song. I like to think that there's something else that needs to be there, something distinctive about aikido, particularly if we're going to use "aiki" as an adjective. Matching, blending,
engaging with the physical/emotional/spiritual energy of the opponent in order to restore the harmony of the universe fits the bill for me.