The tiny turtle nesting island of Pulau Talang Talang Kechil just off the coast of SW Sarawak is the only proven location in Borneo of Ficus callosa south of the Sabah border. Ficus callosa is locally common in Sabah in coastal areas around Kota Kinabalu, Sandakan and Tawau. Ficus callosa is also common near Kota Belud and Tenom. Satellite photo from Google maps.
Teijsmann did not visit Borneo on his 1859-1860 Moluccas expedition so the listing of Borneo is likely a location error. The famous Dutch botanist Teijsmann only made one expedition to Borneo from his base at the Bogor Botanic Gardens (Buitenzorg). This was in 1874 when he collected herbarium specimens along the Kapuas river and around Sintang and Pontianak in West Kalimantan.