If you are a student and your father get news that you have got Grade C in maths exam then most probably your father get upset on you. But in this case, by knowing that his son got Grade C, he starts crying because of happiness.
The boy explaining his father’s reaction and saying that one year back he got Grade F n maths which is said as fail, but in this year he got Grade C which means, he is pass. He also said that “no one has thought that I am going to pass in this exam, nor me nor my father and even my teachers too. But the result amazed me and my father that I passed my exam. Hence my father started crying with joy.”