My apologies, I was referring to a different version of the source code.
In ANT_control.cpp, you will find the comment "Using public network, so no need to set network key", this indicates the demo will be using the default network key, and chooses to not call the ANT_SetNetworkKey() function to specifically configure an ANT network key.
You can call ANT_SetNetworkKey() in the ANTControl_ConfigScanningMode() function to configure the network key before the channel parameters are configured.