Spontaneous numlock

[dsimic]

I'm wondering, if this is on the main board, how is it proprietary to the keyboard and touchpad?

That's a good question.  I'd say that putting the controller chip off-keyboard was a space-saving measure.  The intention of the keyboard designers was surely to make the keyboard as thin and flat as possible.  Placing a small PCB with the controller chip somewhere inside the keyboard would have surely resulted in a bulge, increasing the overall/maximum thickness of the keyboard.