The linked document connects their work to physics as follows:

"The Hopfeld network utilises physics that describes a material’s characteristics due to its atomic spin – a property that makes each atom a tiny magnet. The network as a whole is described in a manner equivalent to the energy in the spin system found in physics, and is trained by fnding values for the connections between the nodes so that the saved images have low energy"

"Hinton used tools from statistical physics, the science of systems built from many similar components."