I don't know the source, but I imagine they're comparing efficiency against a conventional plane flying at sea level. There's no way this can compare to flying at altitude - I mean, the fastest this thing can fly is far below stall speed at altitude - but its key advantages at sea (particularly for littoral defense against strike groups of surface ships) are that it's essentially a ship and a plane in one, doesn't need an airfield, and can hide from radar. (Given this, I'm actually surprised China hasn't been interested in this technology.)