Here's Motorola's statement:

The typical battery capacity for Moto 360 is 320 mAh and the minimum is 300 mAh. In the mobile industry, sometimes both the minimum and typical capacity is listed on the battery, with the typical capacity quoted as the official battery size. Both figures are included on the batteries of our Moto X, Moto E and Moto G devices. In the case of smaller devices, we aren’t always able to list both figures. For Moto 360 we only had room for one figure and choose to list the minimal capacity of the battery. We see how this can be confusing and we will look into ways to add the typical capacity as well in the future.