No I did not make a mistake.

Check in mist :
enter 5e18 in bet
you get 26000000

And it's not a rate.
It's the value of diffculty in the equation.

bigNumber * difficultyMultipler % difficulty_ == 0


So the hash number * 1000 (diff multipler) has to be a multiple of 260000000 for you to win.
1 chance over 260 000.

I know solidity. I did not make a mistake.

This game is a scam.