It works by employing a removable sink insert that empties into the tub, which is in turn angled to help drainage. The lip of the tub, and thus the edge of the sink, is tall enough that it comes within range of the height of a standard sink basin, about 32".
The sink reminds us of tub covers we've seen in Japanese bathrooms. The design could also facilitate greywater use, if you use a mild, plant friendly hand soap.
Images: Yanko Design