"Non-deterministic" in the sense that a dice roll is when you don't know every parameter with ultimate precision. On one hand I find insistence on the wrongness on the phrase a bit too OCD, on the other I must agree that a very simple re-phrasing like "appears {non-deterministic|random|unpredictable} to an outside observer" would've maybe even added value even for less technically-inclined folks, so yeah.