If your device used the hardcoded ABP keys then it probably wasn’t provisioned yet, causing it to use the hard-coded ABP parameters.
Please note that the setappeui command is only valid if you reprogrammed it with the default KISSLoRa-demo_app. If you used one of the examples that use LoRaWAN communication then the OTAA parameters AppEUI and AppKey need to be modified in the code itself.
The command I mentioned sets the AppEUI to all zeros causing the KISSLoRa-demo_app code to use the ABP parameters devAddr, nwkSKey, appSKey as set in the code. This is no longer supported in the current code, I guess the developers don’t like ABP 
Best way to understand is to read the code off course. Probably the authors didn’t intend the use it this way, but it is an easy way to change from OTAA to ABP (but note the disadvantaged of that as mentioned above). Note that the links above might become “off” when the code is changed in the future