I have given my old iPhone to my son who has his own GameCenter ID. It has been signed out by myself, and signed in with his account info. When he opens Clash of Clans, a pop up asks if he wants to load his village. He does, but it says: "Warning: progress in the current game will be lost." Then it asks you to choose Cancel or Load. He chooses Load. Another popup reading: "Are you absolutely sure that you want to delete the current village and replace it with: my son's name"
Does this mean that if he accepts, it will overwrite the village on my account with his?