I'm amazed they can measure the distance between two real non-fixed components down to a few micrometers (they wrote 0.635mm, implying somewhere between 630um and 640um)

If 0.635mm (an odd number itself which happens to be exactly 1/40th of an inch, or "25 thous" in American sizes) and they let it go that sounds really odd. That's literally the size of a grain of sand. If the concern is rubbing, sure that implies it will move during flight.