NonDirective means, literally, “not directed”. It’s an expression of freedom. It was first used in psychotherapy where the therapist didn’t “lead” or “guide” the patient in any particular direction during therapy, but instead allowed the patient to speak freely and in an unguided manner.
Later, it was used to describe forms of meditation where the practitioner didn’t “focus” or “direct” his mediation in any strong way, such as on the breath, but again, allowed the process to freely flow, with an acceptance of whatever results it produced.
Here, we’re talking about music that is made in the same way. Music that is from the soul, the heart, and isn’t overly calculated, but comes from the core of the human being – the music maker him/herself.