I'm not sure I understand the question. Have you read the documentation, both for the example and the library that is linked in the example documentation?
You can see it by checking the current, yes. System OFF is the lowest power state and the current will reflect this. You have to put the device in System OFF mode yourself, this is not something the chip will do by itself. Wakeup from System OFF will trigger a reset, meaning any code after you out the chip in System OFF mode will be executed.
