Isn't that God of the Gaps explanation?

To give a short answer, no, because "God of the Gaps" refers to an unprincipled inference to God. But what we've done here is principled: We have listed out other possibilities of the transcendent cause, and given reasons to reject them. For more that topic though, here's a link to God of the Gaps: Isn’t God just a god of the gaps to fill what science hasn’t figured out yet?