Thanks mate
I'm going to give a very summarised account of Noonan's movements which may shed light on the matter.
Born in 1878 to John Henry Noonan, an Irish immigrant to Australia the family lived in the Bondi area of Sydney in NSW with Noonan attending school in the vicinity. My suspicion is that he came out to South Africa on his own account having not made it into the ranks of the IBC (this is one of your speculations as well) and joined up with the SALH in July 1900 to participate in the war. He seems to have enjoyed his time here as he remained in the country. In February 1903 he was in Durban and recorded as a Hotel Manager when he married a widow, Margaret Lewis born Jackson.
At some point thereafter he relocated to the "Rand" where he joined the ranks of the Wits Rifles (10th Infantry) - it was whilst with them that he excelled at shooting from 1911 onwards until 1914 winning a number of shooting medals in the process. I append photos of these to answer your other question. With war coming in 1914 he was a Lt. with G & H Companies of the 10th Infantry in GSWA - his next of kin (oddly seeing as he was married) was provided as Mrs Noonan (his mother?) of Zulette, 24 Watkin St. Bondi, Sydney, NSW.
He served until the end of the GSWA campaign and then called it quits and went home (Johannesburg). He died in Durban at the age of 80 in 1959. His Estate File records his birth place as Cork, Ireland but mistakes like this made by those identifying the body are common where, as in Noonan's case, not much was known about the deceased.
Cheers for now.
Rory