Yeah, I like him. He is misusing that term but you can't really blame him because Arrma did it too when they labeled the knob. End points or travel limits would be more appropriate for that knob and much easier for a novice to understand.
Dual rates implies two sets of user selectable end points are programmed into the transmitter and selectable with a switch or series of switches (not knob). Commonly expo settings are grouped with these end point setttings and change at the same time with the same switch(es). This feature is very common on aircraft and is something that pretty much every modern air transmitter comes with. Some even have three position switches for it allowing for three different settings. These allow you to adjust how aggressive your handling is mid flight depending on the type of flying you intend to do. A true dual rate setup isn't of much use for most surface vehicles.