Tone refers to the attitude of an author or narrator toward a subject. It is conveyed to readers through word choice. This question indicates that Fallows has a "light" tone in this piece. That is true, but he is also quite serious at multiple places. He has to be, because the article's topic is a touchy subject that could absolutely anger male and female readers alike. It is for that reason that Fallows likely chose to infuse his essay with a lighter tone. One way to create that lighter tone is through humor. Fallows isn't writing a comical piece; however, he isn't afraid to use self-deprecating humor. He calls himself a "lout" at one point:
If my wife, in all other ways a talented athlete, could learn how to throw, I would still have someone to play catch with. My research left some women, including my wife, thinking that I am some kind of obsessed lout, but it has led me to the solution to the mystery.
I think the inclusion of John Goodman's story about learning to become the left-handed Babe Ruth also conveys a lighter tone. We are told that Goodman showed up an hour early to work, week after week, to learn how to throw with his left hand. He was embarrassed by the task and said that he made sure nobody could see him doing this:
"I made damn sure no one could see me," Goodman told me recently.
Most readers have probably been in a similar situation of trying to learn something difficult while remaining completely hidden.