He talks about it directly in the first paragraph, and the entire rest of the article is a rebuke to the standard peak oil argument--and by "standard peak oil argument" I mean things like this--in other words, the idea that when we run out of petroleum, industrial society will collapse.
The article spends much of its time talking about the enormous and growing supply of natural gas, and its obvious future as a substitute for oil. The point is, the disappearance of oil, if it ever happens, is not going to return us to the stone age as the peak-oil cultists insist. Hence, the demolition of the peak-oil argument. The entire article is about peak oil.
He imagines he wrote about it. He wrote about a strawman.