c# - Method arguments reference or not

Question

Could someone explaine please i thought it get just passed by ref when i explicite do it with ref?

var user = new User { Name = "MyName" };
ChangeNameToOtherName(user);      // After method call user.name is "OtherName" < confusing
ChangeNameToOtherName(ref user);  // After method call user.name is "OtherName"

var name = "MyName";
ChangeNameToOtherName(name);      // After method call name is "MyName"
ChangeNameToOtherName(ref name);  // After method call name is "OtherName"