All I know is stay away from ABA. Shit looks cool though

That could be rubberwood, as it's the most porous and less dense wood in the area, holding enough structural strenght to keep strong, and cheapest with pinewood.
I don't know how it would react to water, but a harder local wood wouldn't dilate more in my opinion, as they are much harder / dense, although less prone to deterioration over time.
Available in 1 meter lenght more or less, easily.
Other than that, pine wood, often from discarded pallets, or from a wood dealer (some in Toul Kork)

Best would be teak, as it's oily and very stable in water, but not too sure about availability in Cambodia. Didn't see any fresh cuts.

Other woods, more expensive, heavier, harder, sometime forbidden (Rosewood) international species (Douglas, Oak, Beech etc...) available in Vietnam with MOQ, but overall : available.

Beware of wood cosmetics when buying a big log / slate ^^

Looks good but...
1/ make sure it doesn't become an insect breeding place
2/ make sure the floor beneath it is good. 1 cubic meter of water weighs 1 ton.