As a composer and as a musician I'm a true believer - and this is not to be overly diplomatic - I'm a believer that there's artistry in everything from a lawn gnome to a desk chair to a symphony to an Andy Warhol painting. There's art in absolutely everything.

This quote means that the composer believes that anything can have artistic merit, and can have the potential to be a work of art. Examples given are a lawn gnome, a desk chair, a symphony, and an Andy Warhol painting, but the quote implies that this is true of anything, from the mundane to the extraordinary. In other words, the composer believes that there is beauty to be found in absolutely everything.