As for the OP’s story, it’s really creepy, probably the man was right, because some people addicted to the game will be forced to do things that they would never do in their life and this sometimes causes fear in me.
Gambling is luck and not any form of superstitious believe because even if you believe in diabolic things, there are times when they fail which means it never did existed but you were acting based on luck but if you attach yourself to any form of superstition and it looks as though it is working, a day will come when it will fail you and you gonna lose a whole lot of money. Just take a look at your story about the amulet that didn't work for you but people believe it brings protection and luck so why didn't it give you the luck even though some others might say it works for them but it can't work all the time if at all such believe in the amulet is real. The only thing that makes some people believe that there are some diabolic things attached to gambling is because they got addicted and lost a lot of money and it now sounds as though something was pushing them into addiction just like the story of the OP, why didn't the man make reference to someone else rather than himself.
I have heard a lot of stories about people using diabolic means in gambling and the end result was very disastrous because it's just like a kind of sorcery, it brings good and bad at the same time and the magnitude of evil it brings defeats the good it brings. Do not be deceived, gambling is a game of luck because regardless of how lettered you claim to be you can never be an expert in gambling. If there were experts in gambling, it could not have existed again because people will literally be winning everyday with the help and predictions from the experts.