I think the article is off-base, especially as it combines fantasy and sf together. There are a lot of people who read both fantasy and sf. These folks, I have found (no more scientifically than the article writer,) like to read also outside the categories, though the categories may be their favorites. But a lot of people only read sf or only read fantasy, not both, and many actively hate one category while loving the other.
A lot of sf fans in the past and today are scientists, both social and hard sciences. And these people are predominantly right-handed. It seems unlikely to me that most sf fans are left-handed (though we are suppose to be better balanced on speech.) For that matter, given that lefties are in the minority, it seems unlikely that fantasy fans are predominantly left-handed either. Most of my friends who are fans are right-handed.
Children are exposed to fantasy at an early age, whether they are readers or not. The books they get in school are predominantly fantasy. Television, films, and games are predominantly fantasy. Yet, many kids aren't readers, or if they are, don't like fantasy as children or as adults. Exposure to books obviously has an effect. Exposure to sf or fantasy doesn't necessarily. Exposure to science at a young age may create interest in science fiction.
The main reason most non-readers or mainstream readers say that they are not interested in sf or fantasy is that they think the books are strange, badly written wet dreams about busty maidens and space ships. The category market is dismissed as largely worthless, and fans are still often seen as kooks. The media does nothing to dispell this idea, even though sff has become bigger and bigger in the mainstream. The long-held belief that people don't read sf because they see it as too challenging may have had some mild validity at one point, but I don't think it's as relevant now.
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