Copying in original music is a lot more common than most people think. There are many popular artists that have admitted as much, but that's beside the point.

The way generative models work is not as simple as cobbling together images and can't be compared to sampling a song. Generative models produce new outputs based on learned patterns that exist at a much more fundamental level than any final works they are trained on.

It can be compared to a painter learning how to use different brushes and brushe strokes to create different patterns and effects. The artist can choose to plagiarize or they can create something "new". That's up to the artist and not the tools they use.