I have nothing against digital - when I'm composing and recording music I work entirely in the digital domain (just like 99.99% of people these days), mostly at 24bit/48kHz, and it sounds fine to me.

I wonder what the therapist's clients were experiencing however, assuming the story is true and not just a myth?

At the time I recall the therapist blamed it on the fact that digital music 'samples' sound in many many discrete slices per second, and he felt that the body was aware of that on some level, that the music was not flowing continuously as it does with the smoothly fluctuating voltages of the analog realm.