Can you elaborate on this? If agent A interacts with a system and can learn causal relationships, how could agent B who observes all of agent A's experiments not be capable of drawing the same conclusions?

It seems that any theorem that rules out learning causality from observational data alone would also rule out learning causality from any kind of interactions.

Unless you're assuming that agent A "knows" it has free will so its own actions have no cause, while agent B can't tell whether the environment caused agent A's actions or vice-versa. But if that's what the proof hinges on, it's pretty shallow, because agent A has no such guarantee that its own choices have no root cause.