You are right that the above article doesn't specifically mention the core being functional. I merely interpreted that from one of the stated properties of his

You are right that the above article doesn't specifically mention the core being functional. I merely interpreted that from one of the stated properties of his and the other architectures he showcases: "2. Testable. The business rules can be tested without the UI, Database, Web Server, or any other external element." If that doesn't scream functional, then I don't know what does. :)