It's true that there are many mathematically equivalent ways to describe physical systems. But the important point is that some are more useful than others. For example, Lagrangian mechanics and Hamiltonian mechanics are equivalent to Newtonian mechanics, but they can give much better intuition for certain problems. Feynman diagrams are equivalent to grinding out the QFT algebra by hand à la Schwinger, but they give a completely different intuition for the underlying Physics.

More importantly, though, they could use this NN on systems that have not yet successfully been modeled, perhaps complex dynamical systems, to discover good parameters and conserved quantities.