Guess what? Lowder is not telling the truth! Some naturalists do indeed accept that the universe popped into existence out of nothing. Lowder should have known better. He is after all familiar with naturalist Dr. Michael Martin's works. Dr. Martin said the following (in his own debate with Dr. Fernandes):
According to Dr. Fernandes the Kalam cosmological argument demonstrates the existence of God. This is the argument that (1) the universe began in time, that (2) this beginning was caused, and that (3) this cause was God. I am willing to grant (1) although I believe that this premise is much more controversial than Dr. Fernandes supposes. The other two premises I do not grant. First of all, the universe could arise spontaneously, that is, "out of nothing." Several well known cosmologists have embraced this view and it is not to be dismissed as impossible.
There you have it. Naturalists do believe the universe popped into existence out of nothing. Personally, I don't have that kind of faith.