My guess is that he was simply more successful in whatever he was doing due to his confidence. The book was something he "set his mind to" and did on his own.
The newspaper from the alternate 1985 however identifies him as "local author" so maybe he's a columnist or something like that.
I am thinking the same, sci-fi authors are often published in collections or magazines as serials or one offs, then they get a book together and get it published.
A little tidbit that probably wouldnt have made sense to add to the movie unless they wanted to deepen what George "did" after high school, they sort of showed him as a "writer" in general all throughtout the film, starting with reports in the original universe, then to poetry and whatnot in 1955 to main stream sci-fi in "fixed" 1985.