Technically, it seems to have three different paradigms that it exposes:

> Procedural/Event-based/Declarative - These three snippets achieve the same thing in different ways. One repeatedly asks the button if it is pressed; one tells the button to control the LED; and one tells the LED to follow the button's state.

Much of the article seems to focus on the latter "Declarative" way, which they created a Node-RED-like UI for, which is indeed flow-based. But other approaches seemingly can be used too :)