Pointing with a thumb is a curious quirk I observed in Malaysia. Indicating with an index finger is considered impolite, so it's similar like in Europe. However, as an ex-tour manager who often presented landmarks, I learned to indicate them with open palms. Yet, here in Malaysia, anytime a clerk is showing me a product, they always point with their thumb.

Such an intriguing cultural revelation. Something that can only be detected when you stay long enough in one place.