That "an online AI art tool" in the first sentence is potentially misleading, as the clarification is being made in this article, but this clarification was not made by the artist at the time.

He said (in the Midjourney Discord) that when submitting he "stated that he made them via Midjourney", but it sounds like he didn't make clear that this was an AI tool.

Sincarnate — 26/08/2022 Yes the description clearly stated I created them via Midjourney starshadowx2 — 26/08/2022 Was it explained what Midjourney was though Sincarnate — 26/08/2022 This is why I did it. Should I have explained what Midjourney was? If so, why?

He also mentions that he originally mentioned Midjourney in the caption, but didn't correct them when they edited that part out.

I think these sorts of details do matter.