If what Toru says is true, then perhaps he has finally discovered the “real” Kumiko, which has been his goal since the beginning of the novel. At the very least, he’s reached a new level of understanding and acceptance for the situation his wife is in. Alternatively, everything Toru says could be a coping mechanism. Perhaps the real answer for why Kumiko left is because she was unhappy and didn’t want anything to do with him. However, this answer would be profoundly upsetting to Toru, so he comes up with answers that are more satisfying.