Aashok,
You will need to also look at the Program that created the incident. There can be cases where the file was created in a Program from scratch and then saved to the USB device.
For example if I open Word and create a document and for the first time I save it to the USB drive. Also if I download a file from the Web and save it directly to the USB device.
Also keep in mind that many laptops NOW have Hard Drives that are considered USB devices by Windows and are represented as a device string in the Incidents.
So it is up to the application on how itmight have been created or utilized.
Hope this makes sense.
If this solves your questions please marked as solved.
Ronak