If I remember right I think it's just a silver rupee, but yeah I think @Night Owl is right it should have been off a wooden board, so probably was at the very top.
The correct method is to jump off from much higher up, doing so from a certain point should trigger a free-fall so you can aim yourself better. I'm not sure from where exactly, it was either the halfway point where you first get to the zip line or all the way at the top.