When you get more money on your credit card during a credit card cycle (often between 22nd of the previous month, and the 21st of this month), then you might end up with a positive credit card balance. That means you spent less than you got. This situation can occur when you get a refund for a bigger amount than you spent for that month, for example.
Then you have a surplus on your credit card. But what happens with it? It this case, this surplus will NOT be automatically transferred to your current account. It will be taken into consideration however for the next credit cycle of the next month.