In my view, there seems to be some confusion in the paper between 'discrete' and 'digital': "Furthermore, in the present work, the terms continuous and analog are treated as equivalent in an engineering sense, as are the terms discrete and digital.' [my emphasis]. A similar conflation is seen in several of the quotes from other work in the introduction of the paper.

I think there is a distinction between 'discrete', where the signal is encoded as a non-continuous physical property, and 'digital', which adds the concept of place value to discreteness. This distinction is relevant, for example, where the authors contrast the ability of digital recordings to resist the degradation that analog recordings suffer from. That resistance, however, depends quite substantially on error-correcting codes, for which place-value matters.