I believe this references Pin 10 which is used to connect to the built-in antenna on the standard 20732S/20736S/20737S modules.
Pin 10 on the original SB-01 module was used for an external antenna (this was a larger 8x8mm module) but this functionality was eliminated on subsequent 6.5x6.5mm modules.
However, the new BCM20732E and BCM20736E modules support an external antenna via pin 10 (these are not supported through the community).
So can I understand as below?
"Do not route the GND plane under pin 10 of 20732S".
Correct. That's my understanding.