The absolute zero of temperature is only a point of zero energy in classical physics, which is only an approximation of reality.
In quantum physics it is the point of lowest system energy, which is never zero.
[The simplest, but not always the most correct way to see this is that by the Uncertainty Principle, the ground state of every quantum system that has finite spatial extent (which, for example, descibes anything in our universe) has some non-zero momentum. So "all" motion cannot cease, even at absolute zero.]
They date absolute zero vaguely to the mid-nineteenth century. I don’t think Kelvin lived very far into the last century. It had occurred to me absolute zero predates Einstein and quantum mechanics. I wish they would come out and tell us whether various oldtimey concepts are real, or merely being used to help us rubes follow along.
Or maybe they don’t know, either.
Non-commutation of position and momentum operators.