TOPIC:

Which newspaper(s) would have reported news from your particular village in 1902? It might be worthwhile checking the issues between October 1899 and the end of the war, maybe your man's mention in despatches was reported.

PHSVM
L/Cpl. Mainwaring's superior officer would have noted your man's good work and - in the terminology of my time - "kicked it up the line". A "mention" could be generated by a particular act or good service over a period of time. If, say, Lord Roberts considered a "mention" worthwhile when it came to write his periodic despatches, then it was included. Consider that, at the time, there were few rewards for outstanding service by non-commissioned men. Apart from the Victoria Cross for signal bravery, there was just the Distinguished Conduct Medal. "Mentions" were next in the pecking order.
Some time ago, I submitted a post regarding a Guide in the Field Intelligence Department who was recommended twice for a "reward" due to outstanding active service - but he got nothing. So, Mentions were not apparently given freely.
Perhaps L/Cpl. Mainwaring's inclusion in the Coronation contingent (and receipt of a Coronation medal) was a form of reward? It might be interesting to see if other 3GG men who attended the Coronation were also "mentioned". A newspaper check as suggested might be rewarding.
Good luck
IL.

Ancestry have the Coronation rolls, worth checking.

PHSVM
I am pleased to advise that I have found the reason why L/Cpl. J.Mainwaring was "mentioned". Having a trawl (as one does!) through Lloyd and Russell I found the following references to your man.
On p55, (24/11/1900) "A small detachment, consisting of Corporal Mainwaring and eight men, left Norval's Pont for Hamelfontein. More will be heard later of this detachment, which gallantly upheld the honour of the Regiment". The det. arrived 26/11/1900)
On p57, (apparently 17/12/00) "It was reported and subsequently proved correct that the advance guard of the Boer force had attacked a small garrison of Yeomanry at Hamelfontein under Lt. Fletcher, IY. In this garrison were included Cpl. Mainwaring and eight men of 3rd Bn (GG). Lt. Fletcher stated that this detachment was the backbone of his defence. Two men were wounded while Pte. Mahoney received the DCM in recognition of services rendered. Cpl. Mainwaring was mentioned in despatches".
I don't think you are going to get a better indication as to why L/Cpl. J.Mainwaring was "mentioned".
Best regards
IL.

Nice one IL! I have a QSA to one of the IY defenders who was also wounded.

Thank you, thank you. This is brilliant and your help much appreciated.