Someone going to public library, copying every book out of it and then selling them as their own are thieves.

Not technically theft unless the public library no longer has the books. Selling something and saying you created it when you didn't is a different five-letter word: fraud.

Putting prompts in an LLM and saying you "created" the image or text thereof is fraud.

No, they've merely infringed copyright. Theft is a well understood concept and it does not pertain to information.

I don't believe anything is being sold here :)

Barrels of tokens sold by thieves that copied every book sure looks like selling to me.

AI companies sell access to their models, via subscriptions and ads.

Public libraries don‘t sell anything. Also authors and publishers get payed for having their books in the library (how and how much varies by country). Authors and publishers get nothing for having their books put into AI training data. Hence the former is a public service, and the latter is theft.

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Okay, but that's not what happened as far as I'm aware. Who did they sell their copies of the books to?