It seemed he was trying to argue about the double slit not being evidence of wave particle duality.
I tend to agree, the notion of matter being in two places at once is nonsense.
Also I agree with the author that the majority of people tend to point to the double slit as some type of proof.
Based on what? Empirical experience with macroscopic objects? There are tons of phenomenons that are at odds with everyday empirical experience for that to matter (relativity has all kinds of such cases).
Based on the fact that everything points to the universe being deterministic.
Also we have never been able to even prove it mathematically.
Agreed. Remember he started by saying the double slit experiment has been performed on much larger molecules at this point. People who come across this will go "wait a second?!" and question what they've been told.