Never knew that it was possible to also have in-game transactions in parallel to blockchain. Thanks for the clarification!
Np!
It's quite simple actually, if you think about it.
You give 10 coins to your game address.
The game knows it has 10 coins and that are yours.
In-game you give 2 coins to someone.
It's not necessary for that transaction to hit the blockchain: the game knows you have 8 coins and he has 2.
You withdraw 3, the transaction is regularly sent to the blockchain from the game treasury
Now the game knows you have 5, and the whole game treasury holds 7
That's basically every site handling bitcoins already works, except personal wallets of course.