there are many branches of buddhism. It has origin in India, and India today has lots branches (am not too familiar. But eg idolizing a elephant headed god, you might have seen). Then, China, Japan, and South Asia (e.g. Thailand), has their own variations.
Tibet buddhism, is its own. Tibet is in a high plateau (0.5 km elevation) isolated from the rest of the world. Not until 2006, china built https://en.wikipedia.org/wiki/Qinghai–Tibet_railway that opened the region.