It's his choice and he's - if it is in his own words - articulated it quite well.
The Poppy was for those that died in WW1, but that's changed over the years since to include all wars. And to remember all those soldiers that have given their lives, no matter in what conflict or who was fighting who.
WW2, Korea, Suez, Cyprus, Mau Mau (Kenya), Indonesia, Malaya, Aden, Dhofar, Ireland, The Falklands, Iraq, Afghanistan, Bosnia, Kosovo and Sierra Leonne, all conflicts which involved British & Northern Irish soldiers who died.
We all differ as to who we wish to remember. It's a shame that some won't wear a poppy, but thankfully, those that don't are lucky to have that choice.