Are you sure that's a beneficial mutation?
This from the article:
"The boy is healthy now, but doctors worry he could eventually suffer heart or other health problems."
Doesn't sound like it's necessarily beneficial.
Interesting question. For a mutation to be beneficial, its positives have to outweigh its negatives, over the long run. Throughout most of human history (to a lesser extent today) being stronger and more robust was an advantage for a human. I don't think that advantage is outweighed by potential problems long-term.