I am surprised when an atheist who acts like they have given God some actually brain time asks where did God come from. Even if I was still an atheist or agnostic, I would see the foolishness of that question. Yet, it seems foundational to some evangelical nonbelievers. People who don’t understand the current scientific theories are asking such questions about God. Look, you don’t have to believe. But, when you act like that is some kind of a gotcha question, you aren’t selling atheism to smart people.
I'm never surprised. They have never given God a serious thought. They've never read the Bible and therefore wouldn't know anything about anything in it. They grab a couple verses out of context when it suits them. They're just not serious people, nor should they be taken seriously.
They don't want to understand, either, because there is no room in their life for a real God, since they'd have to resign from the role themselves. They don't know about prophecy and fulfillment. They don't know about healing and answered prayer.
Think about it, though. 2 out of 600k men that saw WITH THEIR OWN EYES what God did in Egypt and THEN in the wilderness for 40 years entered the promised land. 2. Why would we expect anything different for modern folks than those that wouldn't even when they'd seen it first hand?
I've heard every excuse as to why they can't (won't) read it and really look into it in earnest. The bottom line is they don't want to have to change what they do. That's really it. Expecting that from people that want everything for free and not to work is just silly. When they get really sick or lose their jobs, they may even pray, but even if they recover and find work, the last they would ever thank is God.
I've seen it often enough to know.