I don't know this sensei, but this is a video I had seen close to 5-8 years ago. Back then it scifi to me, now out is like "dang that is aikido, he did not give any secret there".
However, at the same time it comes to me that yes it a painless nikkyo, but because he leaves uke free to run away. At the end of his nikkyo the connection disappears. So it is painless because uke is a good uke. If uke was someone really trying to cut nage's head off, would that nikkyo still be painless to be effective?
Thanks for referring to my ancient video. In a way you are right, the nikkyo is painless because uke is a good uke - not a collusive uke, but an uke that is maintaining his attack to the central core. A committed attack is all that is necessary. At a recent seminar given by a direct student of Osensei I attended, the shihan in no uncertain terms recommended trapping fingers as the attacker could let go and re-attack, but I have found that the only reason for uke to let go in the heat of the moment is if his automatic defense system is triggered by nikyo applied as an attack. If for any other reason (he didn't really grab, he was just using the palm of his hand to push keep your appendage out of the way) ki no nagare connection to the attacker's center provides a self correcting point of connection - in other words it means some other resolution will appear rather than the thing we call nikyo - here is a clip addressing that very thing shot a couple of days ago.
Here is an earlier vid from a couple of years ago of one of my students initially regretting he'd never learned how to apply a painful nikyo: http://youtu.be/bVTeiifBbDU