It's not js, it's Processing, which is a simplified version of Java with an elegant, simple API for doing graphics and visual art. It compiles to Javascript via Processing.js.
Actually functions or array being objects internally has nothing to do with "object-oriented" as style of writing code. Here it is about style, which is obviously dictated by Processing (and thus Proseccing.js) being ideologically object-oriented. So, well, yeah, it is quite more object-oriented than "proper" code in js, although I don't see why it is such a problem for the person you relply to.
well, close to. Processing is based on Java, but has a simplified syntax, different visibility model, and different scoping rules. Primarily due to how pde source code gets aggregated into a single class which can be compiled to run in the JVM, but because it's not actually Java any non-JVM implementation of a Procesing runner can pretty much ignore Java entirely and simply implement the much simpler Processing interpretation.