If he knew that his parents would be angry when he told the truth about his big win and received the money, it would be better for him not to say anything about it. Better to save the money for a while and act like nothing happened not to arouse any suspicion from his parents. Or he could secretly invest the money into something more beneficial to him. But there was also another option he could make, which was to tell about his winning honestly.
First of all, what he did was wrong because he didn't follow the order of his parent's but now that he already committed the mistake, I think it will now be easy for him to commit another mistake which is to lie, just in case his parents find out about the money. Im sure there must be other profitable activity that is allowed in his country like investing or trading. He can just say that he got the money from those sources. There might still be people who can feel guilty right after making one mistake and they will confess it right away. They think this will lessen the punishment that they will be getting.
His parents loves him and that's why. His will to take an action should not be cause he is afraid of them he must think about god/Allah first. If he don't care about the creator then fuck his parents no need to worry about them.
Our parents are important because without them, we won't exist but without god there's also no people that will exist. There's even a saying that "god must come first". Maybe it's fine to dis-obey our parent's as long as what they are telling to us is not the same as what is written in the bible.