premise: He interviewed Shigeko Sasamori in December 2004. Ms. Sasamori was thirteen when the atomic bomb was dropped on Hiroshima (August 6, 1945).
hypothesis: Shigeko Sasamori saw the atomic bomb being dropped on Hiroshima on August 6, 1945.
reason: Although Shigeko Sasamori was interviewed about this event, it's uncertain if she witnessed it personally. I think the system is confused because of so many matching words.