When I got a piano again after 35 years, having self-taught as a child, that PDF-book came to my attention in 2008 so 17 years ago. I did not yet have enough playing experience to judge the technical parts. (A few glances now, there are things I don't like.) I stopped reading when I got to a chapter on how to do something that is natural and easy for me, and his "how to" made it difficult and unpleasant. It may have been a part about memorizing, maybe with a melody or themes. I perceive these like sentences, as units. He had this string of pitches, or numerical patterns, or something. In that sense, his being a physicist seemed quite relative, because my mind said "He thinks like a physicist. I'm not a physicist. This is making music hard when it doesn't have to be hard."
Fwiw, I have relative pitch. Some "perfect pitch" got awakened in an exercise I did once ---- by that I mean recognizing A as A rather than the 3rd degree note in a major key having its Tonic on F.