Both statements are correct.
1.The “CLKIN32” is an optional signal. This needs to be supplied with 32 KHz clock input if you want to use the “watchdog” feature.
2.The watchdog timer runs a 32-kHz clock, which may be optionally supplied from an external source on a dedicated CX3 pin(CLKIN32).
I get it now, CLKIN32 is optional for the watchdog timer and reset operation, but if you DO use it, the frequency MUST be 32kHz.