ospi sensor2 – Is it GPIO 23 ?

Am I correct in assuming sensor 2 is attached to GPIO 23. Also why then is GPIO 23 in the free list?
This is from the opensprinkler github define.h.

#elif defined(OSPI) // for OSPi

#define OS_HW_VERSION OSPI_HW_VERSION_BASE
#define PIN_SR_LATCH 22 // shift register latch pin
#define PIN_SR_DATA 27 // shift register data pin
#define PIN_SR_DATA_ALT 21 // shift register data pin (alternative, for RPi 1 rev. 1 boards)
#define PIN_SR_CLOCK 4 // shift register clock pin
#define PIN_SR_OE 17 // shift register output enable pin
#define PIN_SENSOR1 14
#define PIN_SENSOR2 23
#define PIN_RFTX 15 // RF transmitter pin
//#define PIN_BUTTON_1 23 // button 1
//#define PIN_BUTTON_2 24 // button 2
//#define PIN_BUTTON_3 25 // button 3

#define PIN_FREE_LIST {5,6,7,8,9,10,11,12,13,16,18,19,20,21,23,24,25,26} // free GPIO pins