You are stretching "under instructions" well beyond any reasonable definition. The legal system uses a concept called proximate cause to determine responsibility that looks at whether an event cause was foreseeable.
I think this means, practically, people should probably be more careful with LLMs. With humans there's a natural liability shield, because humans are legally responsible for things and have "real" agency. But computer programs are not legally responsible for things. So, with humans, it's not like liability disappears, it moves. But if we move liability to LLM agents then well... it does disappear.
If OpenAI is not liable for the crimes of their agents, then who is? Does the liability just - poof - disappear? Just because it was unforeseeable everyone gets to walk away scot-free and the victim has no recourse, at all, from anybody on Earth?
That seems like maybe not a good idea.