I know it's all settled now for you, but for anyone else reading, yes the officer may grill you, they may even personally suspect that your marriage wasn't valid for whatever personal reason they have. However, in the end if you have evidence to show everything was valid they're going to have a hard time dismissing the case whether they believe or not.
I think most of the the time they act stern as it's probably past the time that doing these interviews is "fun". For what is a big deal interview for you personally it's just another interview for them.