Note that Indonesian dictionaries are written in Java. The root word gamel doesn't mean to hammer. This is sometimes assumed because many instruments are struck with a wooden mallet. The word for hammer is palu in most Indonesian languages. The root word gamel also doesn't mean to hit, or merely to strike something.
Boxers hit, musicians play.
Gamel only means to strike in the context of initiating a defined and intentional sound. The Indonesian word for hit is pukul. The Balinese words for strike or hit include nglantig, ngemplang, and nyagur. When new music came to the Indonesian islands, elements of it were sometimes integrated into the ongoing context of gamelan. The major Indonesian islands including Java and Bali have been demonstrably inhabited by humans for over a million years.