An article: van Leeuwan, T.M. (2014) The enigmatic Sundaland diamonds. Proceedings of Sundaland Resources 2014 MGEI Annual Convention Conference Paper, discusses the diamonds from Cempaka.
One paragraph states: "The Kalimantan diamonds are commonly found together with a mineral suite that includes corundum, diaspore, zircon, chromite/spinel, pleonaste, rutile, and rare tektite (Ubaghs, 1941)"
The Ubaghs reference is: Ubaghs, J.C.H. 1941. Diamonds in Borneo. Report held in Perpustakan Direktorat Geologi, No F 41-2 (Translated from Dutch).
The specimen on the left is also a tektite. The large ~flat face with the single pit in it is an old break that exposed a bubble and has since been partly re-etched by groundwater. Faint flow-banding / schlieren are visible on the left side of the flat surface.
I looked around on Google for a similar tektite; this piece of Darwin glass is somewhat similar, although Darwin glass is generally much more vesicular than indochinites, excluding the Muong Nong layered tektites...