I don't think that this is a silly question at all but a very important one.
We keep muddleing up the issue with "could God change his mind." Most christians would say he CAN but won't. But if it is POSSIBLE to imagine God asking you to do something immoral (whether he would or not) then that means that morality is something that is distinct from God (even if god never deveates from it).
The point of this argument was to determine where morality comes from if not from God. Whether or not God will ever do anything wrong is irrelaevent because God's BEING good is not the same thing as God DEFININIG good.
If God defines good then anything God does, says or commands is right by virtue of God saying it is right, and the rules of right and wrong can be arbitraraly detumined by God. However if God and good are in any way distinct, it is easy to see how an atheist can have morality because a belief in right and wrong has nothing to do with theisum.
Where is the problem? You have already admitted that it is possible o imagine God doing something immoral (even if you also beleve that he would never do it) so you agree that there is somthing we can define as "morality" that is distinct from God.