Pretty sure it is not his oven from the way the blog reads, I would have been more gentle if it had been.
Tulip, as I said there appear to be multiple issues with that oven, but the biggest one as it related to you issue is all that exposed perlcrete. Perlcrete absorbs water like a sponge, and once wet you will never get the oven hot until it dries out. Having an entire oven covered in it, and parts of the oven made of it, exposed to the elements is a nightmare situation if you want to cook pizza in that oven. It's clear to see the oven is not hot by the amount of soot it is covered in. Once an oven is hot the soot will burn off, commonly called the oven clearing.