ISR's priority when MAX_SYSCALL_INTERRUPT_PRIORITY is not used

In the book “161204_Mastering_the_FreeRTOS_Real_Time_Kernel-A_Hands-On_Tutorial_Guide.pdf”, page 255:
If the FreeRTOS port in use does not also use the configMAX_SYSCALL_INTERRUPT_PRIORITY constant, then any interrupt that uses interrupt-safe FreeRTOS API functions must also execute at the priority defined by configKERNEL_INTERRUPT_PRIORITY
As I know if configMAX_SYSCALL_INTERRUPT_PRIORITY is not used, freeRTOS will disable global interrupt when it enters critical section. So, it will be safe to call freeRTOS API in any ISR with any priority?

Ports that do not use configMAX_SYSCALL_INTERRUPT_PRIORITY tend to be systems that don’t allow nested interrupts, and sometimes don’t even have a real concept of a stable priority. I would say the key relationship that must be maintained is the any interrupt that uses the FreeRTOS FromISR API must be disabled when the system enters a critical section, in a task or an ISR (if nesting is allowed).