"You are right, mortise and tenon joints are used in wood working though the idea is similar. A lugged joint would be a more appropriate description. Traditional lugs on bicycle frames have tubes brazed into the lug and the lug itself can be a thing of sculptural beauty. The only benefit I can see here is for the manufacturer being able to save money on shipping costs as a bicycle takes up a lot of space even when partially assembled, which is how they arrive at a bike shop or directly to a consumer. "