The chip puts out signals that are singled ended. It then uses buffers to drive the RS232 pins. If you look at the development kit (part number AN2131-DK001) you will find that we use RS232 buffers to then drive the RS232 lines. If you wanted to go differential you would need to select different buffers. The one on the board is MAX 3232. If you were to select a different buffer (like the MAX3362) you can drive a differential connection (RS422).
To download the contents of the AN2131 DVK please refer to the KB article here.