It seems that the non sequitur you are talking about is this:
"The I explore physics implications of the External Reality Hypothesis (ERH) that there exists an external physical reality completely independent of us humans. I argue that with a sufficiently broad definition of mathematics, it implies the Mathematical Universe Hypothesis (MUH) that our physical world is an abstract mathematical structure." [1]
More specifically, is your concern with this implication?
[\text{ERH} \land \text{("sufficiently broad definition of mathematics")}\Rightarrow \text{MUH}]References