From the apperance, kalang people had a darker skin than the javanese. They also had curly hair.
Why “kalang”? Kalang means border, or “batas” in Indonesian, they were restricted (dibatasi) from kingdom activity (Majapahit kingdom) because their unknown lineage origin so they simply won't fit the hindu class structure..
They lived in rural areas like in the karst hill, coast or on the edge of the swamp. Because of their environment, they turned into strong people. Then the kingdoms recruited them as temple builders, or a workers that require high physical abilites.