A quantum change would be a very very tiny change, something very small. I would say a "quantum" is the contemporary equivalent to what "microscopic" was in the 1800's, or "atomic" at the turn of the century (which at the time represented something so small it couldn't be made any smaller).

But a quantum change in people's thinking, which goes from "panic" to "not panic"? That seems like a state change, but far from an imperceptible -- let alone indeterminate -- state.

Of course the dictionary tells me that a "quantum" is also a very large quantity of something, which possibly makes some sense out of Lieberman's remark, except that he describes it as something that could change quite quickly. That would be to say:

A panic in the market reflects a very large change in people's thinking which can change quite suddenly in the opposite direction, once people realize that the sky isn't falling.

And that tell me... almost nothing.