This is where I disagree. Copyright was most likely violated, but (most likely) because book was obtained not via a legal way.

LLMs didn't spit out Harry Potter until it was prompted to do so. There is argument to be make that LLM can be used as transport of pirated content.

My argument is that it's not different from searching for "file:pdf Harry Potter"

I see your point but it also seems clear to me that somebody violated copyright, most likely the people or company that trained the AI.