The "how on earth" question may be unanswerable. The word "talent" was coined to substitute for the impossiblity of understanding how to analyze, duplicate and propogate those very special abilities.
In America, we are great democrats and like to hope that anyone can accomplish anything with a little extra study and hard work. We throw the word "talent" around to be almost synonymous with "accomplishment."
The Russians, with their highly specialized music education, have a more practical working definition, as it was explained to me, and is interesting to ponder: "Talent" is understood as an ability, either so unique, or so advanced, that it cannot be explained by any known educational process.
By extension, "genius" would be the top of that curve. You can't create a Mozart, you can only get lucky.