It does not require a multiverse. Only for infinity to exist, and probability to exist outside of the universe as we know it. Infinity is a mathematical fact, and probability is an observed, verified phenomenon. God is not. For example we do not know if the quantum foam exists only in the universe or outside it as well. We don't know if our universe has a boundary. It could be that our universe is infinite in all directions. It could be that big bangs happen because of random chance in the quantum foam every 10^2000 years of our time, even in that event, our existence is an eventual certainty- given the one assumption- that infinity exists in time and space.
Assumptions that I share with the very scientists who calculated those odds, I'm in good company thanks.
And you know infinity exists because you can concieve of it, but does it mean that it actually exists?