Father must have money and can provide for his family. He Wouldn't act that way if they don't have enough. Or maybe the father is really a disciplinarian and wanted the boy to stop gambling as well.
A boy having that much in Nigeria can live a life on his own afaik. Fathers can see where this boy is heading and he'll have a say in the family which a father will not like.
You don't know some Nigerians, they are so determined when they set their mind on something, what makes you think that the father must have money and can provide for his family? The father might be an average man living his life with what he can afford but if he insists that gambling money is evil nothing can change his mind, some people believe that money made from gambling can stop you from entering the spiritual realm after you passed away.
I believe this father is a religious man, probably a Muslim that believes that gambling is not a good thing for someone like him and his family, some people loses money while you won their money, this could be the way he thinks.
There is a Muslim man in my home town that disowned his son because his son is into gambling and he the father has tried so many times to stop the son from gambling and the son still keep going back, he ended up disowning his son.