The junction-to-ambient (j-a) thermal resistance figure you cited is for a device that relies on its own body surface to dissipate heat to the surrounding air. The small body is rather inefficient for the job. Any device that has to dissipate appreciable power is supposed to be mounted on a heatsink. Depending on the power level, the heatsink may be a small area of copper on the PCB or a separate piece of aluminium or copper with a large surface area.
The device can transfer heat much more easily to the metal heatsink than to the air, and the large heatsink surface is more efficient at transferring heat to the air. In other words, the device case-to-heatsink thermal resistance is much lower than case-to-air, and the heatsink-to-air thermal resistance is also low due to its large surface area.