Got it ... Here's the part I was missing:

> You will need 4 files from a recent macOS or iOS build:

    neuralhash_128x96_seed1.dat
    NeuralHashv3b-current.espresso.net
    NeuralHashv3b-current.espresso.shape
    NeuralHashv3b-current.espresso.weights

So, for clarity, Apple did not publish the model/code for others to be able to use/test etc. Someone found a clever way to convert the stored model into an open format and therefore others with access to those files are able to experiment.