The users did not access copyright protected data, they can reasonably argue a lack of knowledge of similarities as a defence.

In music that gives you a free pass because a lot of music is similar.

Ed Sheeran made similar music to Marvin Gaye through essentially cultural osmosis of ideas. Robin Thick deliberately took a Marvin Gaye reference and directly copied it.

The legal and moral differences relied on knowledge.

The liability has to fall on who fed the model the data in the first place. The model might be Robin Thick or Ed Sheeran, but given the model has been programmed with the specific intention to create similar work from a collection of references. That puts it plainly in the Robin Thick camp to me.

The AI’s intent is programmed and if a human followed that programmed objective, with copyright owned material, that human would be infringing on copyright unless they paid royalties.