A reporter's greatest reward is when they ask a question the interviewee can't answer. It is called the 'gotcha' moment.
The two Al Jazeera reporters did their jobs well by asking very tough questions and in all occasions, President Rodrigo Duterte answered the questions directly and squarely.
The reason it is very difficult to pin down Duterte is because he speaks from the heart and that he has thought through his position.
Many people will disagree with his answers simply because they do not agree where he is coming from. Take a look at his answer about why he swore at Obama, for many, he is seen as crude but in the end, you will understand that the reason he did what he did was very deliberate. Other lesson learned from the master tactician.