Hi everyone,
Yes, I also guess it is a grounding system for a metal part that may be in contact with a person when the case is on charge by AC adapter. In electricity and electronics is common and mandatory grounding all metal parts for people electrical safety. It would be also interesting in order to confirm this theory, to know if the hinge is also electrically connected to the lightning port metal chassis, if the hinge is made from metal. In case of being plastic, obviously no grounding is needed.