It's best not to pay too much attention to him, because when he loses everything he will look for you, and that's the moment for you to advise your friend, forcing him to talk to him will only cause you heartache.
The Op made the right decision by just standing far away and observing him, and it's even more interesting that the person the player who won the game is avoiding doesn't even care about that, which he had promised him.
If he could have just come clean and said, Sorry buddy, expenses and some other things took away that which was just won, their friendship will just be the way it is," he could have also even gotten free advice on how to effectively manage his funds in case of next time.