Which is absolutely fine? What's wrong with using random art as a placeholder to give a client a sense of what it might look like?

The final image had no plagerism.

I like this comment, "More likely it's a proof that's not AI art - it usually doesn't reuse that much verbatim."

Unless I am mistaken, that reddit poster is accusing the artist of plagiarizing, but the evidence is only from some preproduction reference images and spotlighting elements that are not in the actual final work.

This piece is a commissioned book cover so it would be expected that he slapped together a 'demo' for the author to approve before making the final work.

To be clear, I wasn't trying to accuse the artist of anything, I just updated my post as I read more of the thread and got more information.