Randomness is just one of many possible algorithms generative music can use.
For example: Music for Airports is built from very long tape loops with different durations. It's completely deterministic, but the results sound like a random-ish stream of constantly changing note patterns.
It only works because no human has a long enough memory to hear the loops as loops. If our short term memories could hold a long loop as a percept we'd have a very different and less interesting listening experience.
