I mean, sure, the immediate cause of the NPT was the ability of everyone involved to foresee the possibility of a global nuclear war and judge it both worryingly likely and catastrophic. But I argue that the Hiroshima and Nagasaki bombing was a major reason why this possibility was salient, rather than being treated as baseless conjecture. Whereas right now most people do treat the idea of AI x-risk as baseless conjecture, and this would be different if there was a "warning shot" to point to.