The mouse communicates with the USB dongle over radio, at the 2.4GHz carrier frequency. The mouse uses a modulated laser to identify the current velocity that it is traveling at, by considering patterns in the surface, and sends that information to the dongle using a signal encoding method (e.g. Manchester encoding). The dongle then converts that encoded signal back into the original data, which the driver can then use to extrapolate the current mouse coordinate.
Bluetooth is a particular example of how this communication can be encoded. The Bluetooth specification covers the frequency ranges and communications protocols involved in establishing a Bluetooth link. The actual data sent by the device is arbitrary - completely dependant on the device. Your device may be using Bluetooth, but it is more likely using a proprietary communications method.
Your device uses (one of) the standard USB device drivers. The dongle plugged into the USB socket simply translates messages from the wireless encoding into standard HID (Human Interface Device) messages, which the mouse driver understands. Essentially, the driver doesn't care whether it's wired, wireless or communicating via electrodes in a radioactive monkey's brain - the protocol is exactly the same by the time the driver sees the message from the device.