His Mother's Father served at Rorkes Drift. Any ideas?

By Name/Title
William WARREN, b. 21st November 1908

"In 1927 I began work droving, boundary riding, wheat carting, mustering and general station work on cattle properties. This was followed in 1939 with war service with the Bedfordshire and Hertfordshire Regiment in England. Following the war, I remained in England where I served with the War Office in London until 1956 when I became a Design Engineer with Handley-Page Aircraft at Radlett and the British Aircraft Corporation. I returned to Australia in 1970 and worked until my retirement as a cataloguing officer at the Royal Australian Navy Stores.
All my life I have been proud of the fact that my father served under Lord Baden-Powell at the siege of Ladysmith, and my mother's father served at Rorke's Drift in the Zulu War.
I do not consider myself in any way an Unsung Hero, but I would like it recorded that I did have some years in the outback as a stockman. I dug post holes, did fencing, branding, and ring-barking in weather that varied from drought to flood and bush fires to dust storms.
SERVICE - WAR : With the Bedfordshire and Hertfordshire Regt., British Army.
- DISTRICT : For past 20 years available to schools and community groups for talks on the history of the First Fleet. On retirement, became Honorary Curator of the Experiment Farm Cottage."

"Served at RD" would imply that he is claiming his grandfather was a defender I assume.

Factual error in the writing also, in that Baden-Powell was involved in the siege of Mafeking, not Ladysmith.