If the paper is accurate and not falling prey to false assumptions or some other error we are talking about billions. If we just generalize the deviations claimed by the paper out to the entire world there are about another 3-5 billion humans. If the paper is accurate but doesn't generalize to other countries we are still talking about a billion people.
Because estimating the world population wasn't the point of the paper, and extrapolating their results for the whole world wouldn't be very good science. But discussing something that the paper authors didn't discuss makes a good clickbait title. Especially with the title here on HN, which presents the possibility as a certain fact.