Not an expert, but what I'm understanding is this:
With a regular simulation, whether analogue or digital, you create a mathematical model, and evaluate that model in some way to get a result, which hopefully matches the actual phenomena in whatever it is you were trying to simulate.
Here, it's more like instead of measuring the phenomena, they instead measured something that is physically related to that phenomena. There seems to be no modelling involved.
Like a scale model aircraft in a tunnel, with a fluid that behaves like air, but just enough it can flow slower. Before FEA and CFD, people did a lot of work with miniatures. I remember simulating a long metal rod for an oil rig that was a plastic pipe filled with liquid mercury so that it'd flex the same way the kilometer-long metal rod would.
With a regular simulation, whether analogue or digital, you create a mathematical model, and evaluate that model in some way to get a result, which hopefully matches the actual phenomena in whatever it is you were trying to simulate.
Here, it's more like instead of measuring the phenomena, they instead measured something that is physically related to that phenomena. There seems to be no modelling involved.