That's not 1A off the USB though, that's 1A off the battery, depending on the voltage of the battery and the efficiency of the 5V power supply in the Pandora, more like 500 - 700 mA.
Lets say the battery is at 3.8v, so you are getting 3.8 x 1 = 3.8 watts. 3.8 watts / 5 volts is 760 mA, 760 *...