I seriously doubt that you could manage to start a fire from the device in question.
First the total power of the USB port is ~2,5W on average and given the constraints of the device in terms of size (~ a normal USB thumb drive) you cannot realistically store this more than a second or so (e.g. 100V in 1000µF is only 10 Ws).
With 2.5W you can make things hot to touch, but for igniting anything flamable, you'd have to design some thermally decoupled element to dissipate the power, and get glowing hot (e.g. a small coil of resistance wire in a car's cigarette lighter). Unfortunately devices on a PCB are normally very well thermally coupled to said PCB, so the energy spreads fast limiting the temperature of the individual components. Also things on a PCB tend to break at much lower temperatures than what you'd need to ignite anything. Also they will already desolder themselves at ~200 degC.
That's a good way to start a fire and have a _large_ monetary loss on your hands.