RS422 basics understanding
That's mostly correct except for the part about the receiver having infinite input impedance. It is a differential op-amp so it does mostly just care about the voltage level at the input pins and not the amount of current flowing into the receiver. Wire up a typical op-amp with no feedback and what happens? The output will be pegged to one of the rails. For a communications signal this is exactly what you want to happen. No ambiguity, the output is either full positive voltage or full negative voltage.