It's unfortunate that the article does not provide any source for its central claim. All references in western literature point to quốc ngữ being by far the most widespread script by the beginning of the 1920s, largely owing to the colonial administration pushing for it aggressively.
There was no choice to make by 1945, and indeed none was made.
The population of Vietnam in 1945 wasn't anywhere near 45 million, instead it was a bit under 25 million. This article seems to have been written by someone who only has a strenuous grasp of Vietnam's history, and is very likely confusing the declaration of independence in 1945 with the reunification in 1975.