Essentially if his spending rises due to inflation, as long as his net worth rises, then he's beaten inflation.
If you have a $700,000 portfolio, and you make $28,000 in the market and spend $27,000, your portfolio will be $701,000 at the end of the year, so your nominal net worth has risen. But at 3% inflation, your portfolio would have to grow $21,000 just to preserve its real value, and so your real net worth has decreased. If in 40 years, you have $740,000, you have met your poorly-written goal. Your portfolio may throw off $29,600, but you'll have to consume significantly less in real terms.
I guess what I'm saying is that his spending, rather than his earning, is required to take the burden of inflation because he's adopted such an unsuitable metric. It's also such a narrow period of measurement that it's like he's artificially compressed his time window. By measuring annually, he's put himself in a situation that makes his goal untenable many years, and the amount that he can live on will vary dramatically -- in stagnant years, he'll have nearly nothing to live on, and in years the market actually drops he'll need to spend negative money to increase the value of his portfolio.