I've tried to explain this paper to people in similar circumstances and have also struggled!

In my mind the key point of departure between this paper and the more standard computational functionalist approaches is the importance of metabolism. Metabolism _precedes_ organism. The body is first deeply entangled with the environment through exchanges of resources (content causality) before it is capable of building computers (vehicle causality). Having built and alphabetized the world we can understand them in terms of discrete state transitions.

I expect my explanations have been unsatisfying as we can immediately move to seeing metabolism as some alphabetized input/output system that can be immediately placed back into the computational framework. Moving outside of this framework requires engaging with the enactivist/organicist traditions, which is a rich but minority view.