Negative truth?

In the test, the sentence 'No es verdad que  ________ siempre los papeles al suelo.' gave the answer as 'tiremos', and marked 'tiramos' as incorrect. So does this mean that if you present something as true, you use the indicative, but if you say something is not true, or that the truth is a negative, you use the subjunctive? I thought, in saying it is not true, the sentence was presenting something as a fact, and therefore the indicative would apply.