Nice story-telling. However, in Mahayana Buddhism, Buddha was born enlightened as per the Lotus Sutra and so the Hinayana "enlightenment under the tree" narrative was nothing but skillful means. Also, Buddha is a God-like being in Mahayana, not just a teacher and as Zen and the Samurai are Mahayana, it is important to give the Mahayana version of the Dharma.