I'm sure you will sort him out regardless, however it's the principle. Jobsworth people who have no idea of what is involved here. Instead of looking for reasons why he isn't eligible, they should be looking for ways to get around criteria; when they put the phone down, it should be thinking 'Yes! I really helped a veteran out there'.
Hint: In the USA (whilst not perfect), people go out of their way to find discounts for serving and veteran personnel.
Go to the Daily Mail or Sun, using the words 'outraged and angry', they will hijack your story a little and Boris will probably get involved as well. Its important to all serving and veteran personnel that these London Transport PUBLIC SERVANTS get to know their real place in life.
Question: Why have a ticket available and make it difficult to obtain???????