On the Commonwealth War Graves Commission list, they listed him as Lieutenant and also on this website:
glosters.tripod.com/BoerR.htm
RUNDLE - Lieutenant William John Scott, D.S.O. - 6th Dragoon Guards (Carabiniers)
Wounded at Kareebosch, 19th July 1901. Died at Beaufort West, 30th July. Aged 25. Born 26th March 1876. Son of Dr. George E. Rundle, of Rooty Hill, New South Wales.
RUNDLE - Lieutenant William John Scott, D.S.O. - 6th Dragoon Guards (Carabiniers)
Wounded at Kareebosch, 19th July 1901. Died at Beaufort West, 30th July. Aged 25. Born 26th March 1876. Son of Dr. George E. Rundle, of Rooty Hill, New South Wales.