As a software person who doesn't know much about this sort of thing: how does this work electrically? Presumably there's no current flowing as it's an open circ

As a software person who doesn't know much about this sort of thing: how does this work electrically? Presumably there's no current flowing as it's an open circuit? Is it akin to a voltmeter using the ground as a point of reference? Why don't other wire-based protocols use the single-wire approach? Does it have anything in common with 'single-wire earth return', in power-distribution?