Personally, when I gamble and end up about 3/4 of a million dollars in the hole, I assume that I lost.
That sounds more like a conclusion than an assumption.
But the question isn't "Who won?" It is: "On the basis of this result what can we say about who will win next time?"
I don't know what kind of measures they used, and there are a couple of links in this discussion to papers pointing out how problematic p-values are, but it is perfectly possible for the weaker competitor to win any given competition. All it requires is that the width of the performance distributions be large enough to give significant overlap between the players.
People who don't understand statistics are baffled by this. They see individual instances, but statistics is about distributions. We can, by measuring instances, make judgements about the distributions they are drawn from, and knowing about the distributions we can make predictions about future instances.
In the present case, it appears that the observed distribution of performance was such that it wasn't possible to distinguish clearly between the case where the computer is slightly better than the humans but the humans got lucky, and the case where the humans are definitely better than the computer.