I am not surprised at all about this. I think the population of Asia alone is almost two-third of the world population. That makes it possible to be the highest number of holders too.
You are right but if we think about profit making or money making then there is no Asian and African or European but we the people want to make some money. It does not matter if the start of Bitcoin was from Europe or somewhere else other than Asia but slowly with the passage of time Asians are leading as most investors for Bitcoin. However this is very good if most users are from Asia but users are from Europe too but they should show some more actions.