What is this technique of joining wood called?
They are joined...with wood glue. No, seriously...it actually is "stronger than wood". Bandsawn lamination is about as close as you'll get for a "specific name", though it could also be done with a router and templates. Or a CNC router, for that matter, these days.

The efficient approach will result in this one and a dark one with a light section, by sawing in stacks, then shuffling. This also has veneer strips along the glueline.