IMHO it's just marketing and hype nothing else.
It should have been listed as a "direct" PT because that is all it is, in comparison with the JoyE PT with an in line battery. In this aprticular case, your PT is running off the battery and not the USB port. The USB port is merely charging the battery. The PT will not work with a dead battery, until such a time that the battery is partially charged.
PTs were designed to save on batteries, nothing else. It only makes sense to use a PT while at your PC, saving your batteries when removed from the PC, and although PCs have 5 volts available at the port, they don't have the power e.g the amperage is only 500mA or 0.5 Amps.
You wan't 5V get a wall adapter, capable of producing 5V and 2 amps or 2000mA (yes that is right 2000, most outputs are rated in mA). These sell for $2-10.
All JoyE devices run at 3.1V due to the onboard PCB. What does that mean. It means a constant 3.1V power available to the atty during the battery cycle. You will not see a gradual decrease in production. It is either producing or not. On other devices, the user can see and sense a decrease in production over the battery cycle from charged to discharged.
Before I would make a purchase of such a device, I would ask for some specs, all the specs.
Most USB ports do not put out the amperage to fire these at high volts, regardless.
Furthermore, I would like to have a protection circuit between my device and my USB port, wouldn't you?