Halcon: Your claim that it was God, because God wasn't falsifiable assumes a great degree of thought and mental capacity on the part of its originator.
Only if we presume that the concept was originated all at once, in an advanced/completed form, and isolated from any other ideas. I don't think this is the case. The creation of god(s) was probably a very lengthy, gradual process. Many ideas and explanations would have been offered. The ideas and explanations that could be most easily tested and challenged would have been filtered out over time. The ones that were difficult or impossible to disprove would have held on longer, and eventually been refined.
This is why I think it's notable that there wasn't always one specific god who was put forth as an explanation. The Bible describes a god who was known to some humans personally, who performed miraculous feats that people witnessed, who was known to humanity right from the start. And yet, we find older writings and older gods than the one described in the Bible. We find older explanations for the creation of the world, and older descriptions of how things came to be. It fits more readily with the idea of gods as handy --if useless-- explanations for the unknown.