These are actually Malaysian river driftwood. Since these are collected directly from riverbeds, its hard for the collectors and vendors to properly identify each individual piece. So they lump the entire lot together as "Malaysian river driftwoods".
Mangroves are indeed strong lumber, but since they grow mostly along saltwater shallows, they contain too much salt for orchid and freshwater aquarium use.
There are specific species of orchids that live amongst the live mangrove branches though.