Most likely by way of Quil (https://github.com/quil/quil). Using quil in your ide of choice is a dream and a remarkable improvement over the native processing env in terms of interactivity with the sketch.
It does indeed use Quil and was really happy to see there recent (May of this year) addition of ClojureScript support. It is a great library and made building up this tutorial great fun using the repl.
> This truly was an amazing place. Here, dreams and reality had been drawn together - all in one Process. "_Why would I ever leave?" he barked with joy! _Why indeed!
Is this implying that this framework was the work of _why the lucky stiff, or is it just some kind of reference to him? The description does very much seem like his style.
I think this will be a hoot to play with my cousin starting out. Clojure is a bit more elegant than processing's language, but with the awesome ease of drawing of the processing frame work.
And the documentation's purple prose is just fantastic!