Good that you found the source of the nodename in the DB2 configs.

Yes, mixing API-based and B/A-based backups on the same client will
result in the node Platform designation changing.  Where both types of
backups would need to be performed on the same client, it is best that
the B/A client use the natural hostname for the nodename while the API
employs a fabricated, indicative name.

  Richard Sims