Purpose of inverted channel for UART bus communication
More than likely it's a balanced-differential data transmission. This offers much superior noise immunity on long lines compared to a single-ended data transmission system. It also doesn't generate the interference that a single-ended data transmission generates because E and H fields cancel. But it requires (for optimum performance), a differential signal that is transmitted simultaneously on two balanced wires such as twisted pair for example: -



Picture from this wiki page.