So Mark Zuckerberg had to face the senate regarding Facebook data leak. It is said that Zuckerberg was briefed by his lawyers, consultants and advisers before the hearing so he was well prepared to answer all possible questions. He knew quiet well what to say when and when to take a step back and request to come back regarding additional info. he knew about his rights.
The congress lawemakers on the other hand were quiet unprepared. They did not know clearly how facebook worked and also were not clear on what and how to ask. Many questions were related to how facebook worked (so it was evident that the lawmakers were clueless of facebook's business model). A good amount of time was spent in asking and answering such bogus questions. Some suggestions on security that were given to Zuckerberg were already on facebook. This lack of knowledge of modern technology, of how facebook worked etc., by the lawmakers and gave a position of authority to Zuckerberg who was well prepared and am sure was taken aback by the questions (more like he was expecting to be badly grilled but it turned out it was a joke).