This piece was created using Magenta Studio. It's a plugin which uses machine learning to generate MIDI, all the input I had in the composition personally was to give the MIDI a sound and an arrangement, the rest is entirely based on the machine.
"Magenta Studio is a collection of music plugins built on Magenta’s open source tools and models. They use cutting-edge machine learning techniques for music generation." Find out more here: magenta.tensorflow.org/