At eighteen, the boy is an adult and would take full responsibility for his actions and inactions. Parents indeed need to closely monitor their children's activities online, but at that age, it will be very difficult to watch over that boy. This child simply chose to be a criminal, maybe he was influenced by friends or other agents of socialisation.
For me, if a child is still under my roof, I would closely monitor their income and expenditure. If he is spending more than I think he should, it will be the right time to investigate his sources of income. It is also important to always investigate the source of your children's income. Don't rely on what he or she told you.
For sure, there's no much to doubt here. That boy is simply acting under the influence of his fellow friends and of course under the guidance of a superior among them. It's questionable to see a boy of that age too clever to indulge in that act and even attempt to deceive his dad on what he does for a living. Sincerely speaking, some parents are too careless to neglect the financial aspects of their wards. They don't care to know the legitimacy of their hustling as long as they are giving them money to cater for themselves.
It's unfortunate the young boy get to know about Bitcoin in the wrong way and also making use of it wrongly. Their types are the reason why some people have a negative perspection on Bitcoin and assume everyone who's into bitcoin is a criminal.