Tonus-I don't know if god was always the explanation for the unknown. It may have been the most convenient explanation because it wasn't falsifiable. If there was a single being responsible, one would expect that every explanation would refer to this specific being. But, over the course of human history, entire pantheons were invented and catalogued and used to explain the unknown.
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.
Assuming that the first human being who came up with the idea of God was very primitive, this same primitive had to weigh an impressive amount of pros and cons, data, variables etc in order to formulate and arrive at an unfalsifiable God in order for the idea to stick. That's impressive for a supposed 'caveman'.
In fact it was such a stroke of genius from that primitive that this notion of God still exists today, eons removed from all the ignorance that once existed.