There should be some SCOTUS case where this limitation on the First Amendment is defined if the law doesn't work like that.

I mean, back when Constitutional law meant anything to the government, of course. Nowadays who knows.

> limitation on the First Amendment

This suit has nothing to do with free speech and the F1A provides no relevant protection here. This prosecution is under consumer protection law. Broadly, the cause of action is "you negligently sold a defective product which you knew (or should have known) actually causes harm or is likely to cause harm." Proving negligence (willful or otherwise) depends significantly on things like the sales and usage context as well as claimed features of the product along with disclaimers, disclosures, existing practice, prior knowledge of actual harm, etc.

That the product or service in question included supplying information that was publicly available elsewhere wouldn't be an effective defense against claims of willful negligence or reckless endangerment. For example, rat poison is sold in in certain retailers in packaging with copious warnings and successful prosecutions under product liability or consumer protection law are rare. But if another company sold rat poison in bright pink boxes with a cute cartoon mascot and no warnings in toy stores - and then kept selling it after they knew three children had bought it and died - the fact the same chemical compound is commonly sold in hardware stores wouldn't be a very effective defense.