Mamy....not liking all fruits because they are called fruits IS irrational.
My niece will eat tomatoes, but we are afraid of telling her that they fruit not veg, just in case she adds another foodstuff to here hate-list. She briefly liked melon when she was much younger, because she thought it was a vegetable, but was put off when she found it was really a fruit.
In my experience, children develop these strange eating phobias as a way of controlling adults. The same niece spent the ages of 7-8 only eating baked beans, until my brother stepped in and took control over his wife's "anything for a quite life" attitude.