Just a question here. Do you think many Thai forest teachings and Zen teachings are similar because they are both fundamentally meditative traditions? The Thai forest tradition doesn't reference the Pali canon as much as say, the Burmese or sri lankan's do, and Zen doesn't cling to mahayana sutra's as much as Tibetans and Pure lander's do. They are both traditions that practice finding out was is true for yourself.
This is a very VERY lay person't observation, but do I have a point?
"The original heart/mind shines like pure, clear water with the sweetest taste. But if the heart is pure, is our practice over? No, we must not cling even to this purity. We must go beyond all duality, all concepts, all bad, all good, all pure, all impure. We must go beyond self and nonself, beyond birth and death. When we see with the eye of wisdom, we know that the true Buddha is timeless, unborn, unrelated to any body, any history, any image. Buddha is the ground of all being, the realization of the truth of the unmoving mind.” Ajahn Chah