The confusion clears up if you stop conflating contextual conditioning (prompting) with actual Learning (weight updates). For LLMs, "few-shot prompting" is technically a misnomer that stuck; you are just establishing a pattern in the context window, not training the model.

In voice cloning, the reference audio is simply the input, not a training example. You wouldn't say an image classifier is doing "one-shot learning" just because you fed it one image to classify. That image is the input. Similarly, the reference audio is the input that conditions the generation. It is zero-shot because the model's weights were never optimized for that specific speaker's manifold.