As Car Dr has indicated, it's saying there was a fault detected in the HV battery supervisory circuit A. This would be either as wiring, harness connectors or electronic components. All this is based on my reading of an early 2017 shop manual for the PacHy which I bought when I got my PacHy in May 2017.
There is also a circuit B. These two are supervisory circuits which appear to be used to communicate information from numerous other sensors within the HV battery. There are many other diagnostic codes for the battery pack which would indicate problems via these sensors if temperature, voltage, current or other problems exist. The service manual indicates the vehicle may shut down if this code is set. Fortunately, that didn't happen in your case.
These circuits are internal to the HV battery assembly and, since FCA considers that assembly not repairable at the dealer level, apparently all they can do is disconnect external harness connectors to the HV battery pack (presumably related to the battery pack control module?), inspect them and reseat them.
In my opinion, the dealer can/should hook up the diagnostic equipment and check for pending codes as well as other data to investigate this problem since it could shut you down on the road if it reoccurs. Based on the diagnostic procedure in the service manual, it does not appear they will replace the HV battery unless the DTC returns after the harness connections are checked.
I agree with you that the dealer's initial "Don't worry be happy.." response is terrible. Hope the above helps & good luck.
2017 Silver Teal Hybrid
2014 BMW i3 REX
2005 Grand Caravan SXT
2003 BMW 530i
2000 BMW 528iT