Windows has Autoplay which can fire up Bridge to auto-import pictures as well. In my case it was Lightroom.
This happened to me a few days ago. I plugged in a usb stick and Lightroom opened up and started importing my Pictures.
The Windows program is called Autoplay. You can find it in the Control Panel and set the default actions.
AutoPlay: frequently asked questions - Windows Help
Sure enough, Lightroom 5.0 somehow set itself up as the default for auto-importing picture files.
Gene