Actually Dr. Jacob R "JR" Mittleider was doing this years before Mel was even out of diapers, basing it on over 55 years of his own studies and personal gardening experience. I believe he called the method the "Mittleider Method of Grow-box Gardening". But whereas Mittleider (world-renowned ag consultant) conducted most of his program efforts outside the US in trying to teach people of 3rd world countries how to feed themselves, Mel capitalized on it, right down to "custom" soil mix and the trellis setup/design, and marketed it as his own under the phrase, Square Foot Gardening.
I have several of Dr. Mittleider's books (pre-1980's) as well as Mel's SFG book, and while I refer to both authors, I prefer Mittleider's works. And not that I'm garden illiterate (quite the contrary), but Mittleider's writings are easy enough to read/understand and chock full of diagrames/drawings/photos so that even those with little to no garden experience and few resources (again, think 3rd world countries) can grow productive gardens.