So if this wasn't during WW2, how exactly was he protecting the farmer other than in the same generic sense in which the farmer was feeding him?
Most Western militaries spent most of their time after WW2 doing other things than defending their nations' citizens so the question seems valid. I'm not initimately familiar with the UK's 20th century military hijinks but the only two significant conflicts I can think of were the Falklands (which seems to have pretty much exclusively been fought overseas) and the Troubles (which fighter planes wouldn't have helped with).
It's just a misunderstanding I think. It sounds like the OP's dad was in the RAF during the war, and "risking his life to protect the farmer" was a reference to that rather than the particular flight he was on when he had to make the emergency landing in the field.
So I can sort-of understand why they are being defensive. In their eyes there are commenters denying their father's effort in the war. But the commenters were actually either trying to understand if there's an extra story or were puzzled what kind of life-saving flights could be conducted in the British mainland in the years following the war.
Most Western militaries spent most of their time after WW2 doing other things than defending their nations' citizens so the question seems valid. I'm not initimately familiar with the UK's 20th century military hijinks but the only two significant conflicts I can think of were the Falklands (which seems to have pretty much exclusively been fought overseas) and the Troubles (which fighter planes wouldn't have helped with).