Is this aikido? Not that I would expect the person that did the disarm to move to the front. Not to question what he did. But is it aikido?
Japanese arts deal with things like Sen. Stanley sums up here well.
“Go no Sen” — The Path to Defeat by Stanley Pranin
There has to be committal from an opponent towards you yourself. You then use that committal against them. It "must" be seen, even for a split second. In seeing that physical action it mean they have already committed themselves mentally to a point of no return. Aikido is not the only art that uses this method.
The idea in practice is to try and simulate a real attack. A method that can be speeded up as people become more proficient in dealing with a situation. Ultimately as seen (should be seen) in embu we really attack. Even then we still have the perogative of knowing what is coming.
There are others that use "sen only". Some incorporate it among other methods such as simply attack first feign an attack etc. etc. But sen remains to be the epitome of most of the arts.
The point is if two people confront each other and the one using sen sees no attack? Then there is no conflict. We can all safely go home.