It's a scam because he says "You will be able to earn bitcoins and double them" which isn't true.
Where does it state that? Not on the site...
In OP:
You will be able to earn bitcoins and double them in a matter of days. All youll need to do is follow the rules of the game.
Most people will lose.
You're definitely right about that, because the OP is honest enough to admit that it is a ponzi scheme.
Yet he claims you will be able to double your coins. That's not honest.
On a gambling site you know that in the long run the house always wins and you will lose, does it make gambling sites a scam? No, only if they would rig the games.
Or if they said "you will double your coins if you play here". They don't say that. If OP didn't say that, he wouldn't be running a scam either. But he does, so he is.
Get it yet?