I can shed light on this whole thing
It is a cable for the leds on the hp monitor stand. hence why it called monitor stand port.
As per the description in the product details in the link, it says that the monitor stand lights up when laptop on on and docked etc. just like the docking station does. It is because when it is in the stand, you couldnt see the lights on the docking station as it sits at the back, under the monitor.
Took me alot of research and thought to figure this out!