Do you know why does Suganuma steps back every time he completes a technique? Is that an Aikikai "thing?"
Well.. aikido is best displayed when there is a distance between uke and nage so that nage can gain momentum for the attack, and I believe they want to stay within the camera angle, so my guess is he is getting into a good position to receive the next attack.
In beginner training walking backwards is not encouraged (at least not in my dojo). In a situation with more flow you take the steps necessary to stand in the best possible position taking all attackers (and cameras) into consideration..
At least that's how I would interpret it.