Exactly. The site mentions that and some other problems, and just disclaimers their liability. One problem I didn't see mentioned directly is that some venues have additional bureaucratic rules.

For example, I saw a writer-artist complain that they couldn't show the big ebook store proof that they'd licensed the art for their cover, since they painted it themself, and there was no documentation licensing it to them.

So one could use practical advice from someone who's figured out the rules, and has the battle scars, like: "With public domain art, just make sure you do X and avoid Y; otherwise, there's a 50% chance that a random copyright check the first week will result in your book temporarily being shadowbanned, and you won't get the crucial early sales while the algorithm is trialing exposure of your book in searches and categories, and then the algorithm will pretty much never show your book to anyone ever again."