Right click is also considered a key in the controls menu, buddy.
The server cannot detect when any random key is pressed. If you press a key that has nothing bound to it, the server will never find out about it. Keys that only perform client sided tasks, such as opening the escape menu, also don't send anything to the server. Right click, when pressed, calls the method armor::onTrigger on the server. "L" when pressed, it calls the function serverCmdLight. Secondary fire options work by modifying those functions and checking if a certain weapon is equipped. If the weapon is equipped, it will replace the original functionality.