You don't really need to have a radio button array and an additional Submit button to create a True/False style of question that can report to the quiz.
There are only two options for a True/False question. That means you can pose the question with a text caption and then just have two buttons underneath. One for True and one for False. Only ONE of these buttons (the correct answer) needs to be given a score and set to report to the quiz.
So if the answer should be False, you set the True button to NOT have a score and NOT report to the quiz, but the False button DOES get a score and DOES get set to report to the quiz. If the learner clicks the wrong button they get no points added to their quiz score. Only if they click the correct answer does their quiz score advance.
A True/False quiz question done this way can be done multiple times on the same slide whereas the traditional T/F question format in Captivate only allows for one per slide.