If I memorize the text of Harry Potter, my brain does not thereby become a copyright infringement.

A copyright infringement only occurs if I then reproduce that text, e.g. by writing it down or reciting it in a public performance.

Training an LLM from a corpus that includes a piece of copyrighted material does not necessarily produce a work that is legally a derivative work of that copyrighted material. The copyright status of that LLM's "brain" has not yet been adjudicated by any court anywhere.

If the developers have taken steps to ensure that the LLM cannot recite copyrighted material, that should count in their favor, not against them. Calling it "hiding" is backwards.