Už jsem našel popis čipu, který je na té kartě použit pro PS/2. Takže to je opravdu přes USB.

The CEC CSC0101A is an integral micro-controller for converting PS/2 interface signal to USB applications, which includes 8 bits high performance micro-controller core, combined USB1.1 low-speed interface and dual PS/2 handler module. It is ideal for the legacy system support, enabling seamless connections of traditional PS/2 interfaces devices of mouse and keyboard to USB.

The CSC0101A is a USB 1.1 low-speed compliant device that interfaces to PS/2, it support the Human Interface Device (HID) class specification. The CSC0101A handles the merging of the PS/2 data and sends the data to the host system via the USB port