Christians!! Answer this!! Something from nothing?

Why do Christians that are against atheism believe that atheists believe that something came from nothing? That is not what the atheists believe, we believe that the universe originated sometime between 10 billion and 20 billion years ago from the cataclysmic explosion of a small volume of matter at extremely high density and temperature. The idea that something came from nothing is actually the Christian belief. Christians that believe in Creation think that God who magically has existed forever created the Earth out of nothing in the span of three days and in one day created the rest of the universe out of nothing which we now know to be BILLIONS of light years in expanse.