@Zheng-Han This makes a bit more sense.
However:

I note that the picture of the physical switch actually shows a fifth solder connection - between 1 & 2 in your picture - and I observe that this is soldered on my Expansion Dock I still don't understand just how this all works and how the switch is actually connected. @Lazar-Demin above says that the RESET_BTN is connected to ground when the button is NOT depressed. I still don't see how this works given the circuit diagram and your description of the button