Question: would she be so disheartened and mad as this if the son had won the bet on a multi million price?
Dear fellows, let's assume you are the mom, what would be your state of mind on this context?
OP, you did not mention the age of the kid, and perhaps if this was a case of underage gambling, I think the parents should be blamed for not paying much attention to their kid, which led to his becoming addicted to gambling. This kind of habit that was exhibited by that kid shows that he is either a compulsive gambler or he is yet to become one.
If the child is not under age, then he is now a fully grown adult and should face any discipline that the parents would give him. If this is the first time he is exhibiting such character, then he deserves to be forgiven, and let his parents caution and advise him.
If I were his parents, I would get angry with him, but I would still forgive him. I would then try to advise him about his compulsive gambling habit, and I would try my best to help him learn that gambling addiction will not give him a better future but might end up ruining his life. If, after all my advice and help, he refuses to change, then I will not allow him access to my money.