The 4 ship of Hornets was one of the many taskings for Australia Day - Melb, Syd, Adel and the central coast. The Melb flypast you mention specifically was tasked for the parade on Swanston St (1135) and the Shrine (1138). No doubt some nice work on behalf of the boys involved to have auth'ed a trip around the Bay and back up the Yarra!