That's because he is. Take a look at the articles listed on his website.
Science can't tell us so far what really exists. It can only predict experiments. To put it in more common terms, "is the wave function real or not?", or "do quantum fields really exist, or are just elegant mathematical abstractions for explaining experiments?"
Or as others say "shut up and calculate".
Your "only" here makes it seem like predicting experiments is a narrow thing. It's not. All of the modern technologies we have--including the computers we're all using to post here--are based on science "predicting experiments"--but the "experiments" are things like building computers, or the Internet, or the GPS system. The fact that all those things work exactly as our science predicts makes it very hard to view that science as "only predicting experiments". It's telling us how to use real things to build real technologies that have real impacts on people's lives.
A religious person - if not honest enough to simply say "existence of God is an axiom and cannot be derived from reason alone" - uses the very predictions of experiments to reason God into existence: everything that exists has a cause; universe exists; therefore universe has a cause.
Only inasmuch as nothing can tell us what "really" exists. By any practical definitions of any of the words in that sentence science is the best way of determining what exists.
So not quite chemistry, but particle physics?
The article does focus on particle physics, I think because that's the most fundamental level of physics we have--everything else is built on it.