"Are you pregnant?"

Once upon a time, when I was young and innocent, I had to have some X-rays taken. "You are not pregnant, are you?" - asked the X-ray technician. "I don't know, but this is highly unlikely," - I answered, - "and it doesn't matter anyway, I'd have an abortion if I were pregnant".

She really did not like my answer. Now that I am old and wise (haha) I sort of know that you are supposed to answer "no" if you are using birth control and have not missed any periods, even though you really don't know. But I still don't quite understand what's wrong with being more exact and what was her problem.