First of all, I have never head the term "book liar" so please don't think this is a commonly used expression.
The answer is "He is a book liar because he said he had read a book but really had not." Your answer doesn't make sense - they are talking about the book, not other things about the president.
It would be astronomically improbably that the exact same survey respondents who had not read 1984 were the same ones who read the ending of a book early.
If I asked ten people their favorite color was and 3 said, and then I asked what their favorite flower was, and three said it was a daisy, I can use 30% for both, but they do not have to be the three same people.
Student or Learner