Yes.
The incident took place during the Boer War period, when the
Medic was on the Australia run. Lightoller arranged to raise the Boer flag and fire the gun on top of the Martello Tower on Fort Denison - a tiny little fort in the middle of Sydney Harbour. You can read about the incident in some detail in the Stenson biography and Lightoller's own autobiography.
Pat Winship did an excellent write-up on the 'One Gun Salute' incident, and published an article in the
White Star Journal about it a few years ago. I did a bit of background on it and found references to it in Hansard (State Parliament) and contemporary newspapers.
A member of this board, Fiona, has told me that the incident was mentioned by the guide when she did a tour of the Fort a couple of years ago.
I'm very fond of Fort Denison and its history, and think of Lightoller every time I pass the Fort on a ferry or in a sailboat (and have told the story to my companions more than once!). Once, attending a reception at Government House, I tried to imagine his daring escape through the grounds after their escapade nearly came to a disastrous end.
There are many images of the Fort online: