Hi! Author here. You're right that music and speech carry more than just raw symbols such as intonation, pitch, dynamics, etc. all add important information. But in the framework I'm using, both are still fundamentally “1D” because their core structure unfolds sequentially in time: notes in a score, words and phrases in speech. Even when additional features like accent or dynamics are present, they're layered onto a linear stream.
Recto, by contrast, makes two dimensions part of the syntax itself: elements and rects can expand horizontally or vertically, and they can nest recursively. That's the difference I wanted to highlight.