"They then copied those stolen fruits"

How are these fruits "stolen" if they still have what was allegedley stolen?

Dowling v. United States, 473 U.S. 207 (1985): The Supreme Court ruled that the unauthorized sale of phonorecords of copyrighted musical compositions does not constitute "stolen, converted or taken by fraud" goods under the National Stolen Property Act

And even if, arguendo, sure its stolen. The purpose of copyright is to "To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries"

And you would be hard pressed to prove that LLM's haven't advanced the arts and sciences, so at bare minimum transformative, ie fair use.

I think you are confusing the idiom "stolen fruits" with an actual accusation of criminal theft. Aside from its use in this phrasing, neither "theft" nor "steal" appears anywhere else in the article.