The #1 thing to do after playing at any BTC sites is enabling 2FA. Just a small mistake can cause you to be hacked and because it's so easy to cash bitcoin out, it would probably mean your coins are gone. It's the responsibility of the player to make sure they are doing what they can to ensure something like that doesn't happen.

Could it be you clicked a malicious link? Anything could have happened. I'm sure it's not a flaw on the site.