If I am understanding the article correctly, there is no hidden variable implied. Quantum physics claims changes are random, with nothing precise and determinate underneath that causes this.
Think of the example of flipping a coin. It's random, but for each flip if you had exact data for the movement of the coin as it left your hand, you would presumably be able to predict if it would land heads or tails. Quantum physics claims that for events at the quantum level, there is nothing definite underneath that determines what will happen, it is just fundamental randomness. The hidden variable idea is that there is something definite underneath, we just haven't discovered it yet.
What the experiment seems to have found is only that the probability of an event occurring changes smoothly over time from 0 to 1, not that there is some underlying exact cause for what the probability is at a given point in time.
They detected a quiet period of slower transitions before the spontaneous drop to the middle state... this implies that "something" happens prior to the transition.
They were able to detect this "something", and even prevent the state change.
In my mind, that "something" represents a hidden state or something like it within the synthetic atom.
The trouble is there are some strong arguments against that idea, so quantum physicists tend to assume that such "somethings" just don't exist. Yes, that is very counter-intuitive, but that is one reason quantum physics is so weird.
There seems to be some sort of "hidden variable" there... can anyone explain it?