It seems to me that Malcolm Gladwell is talking about experts rather than genius. Genius is more innate and discovered, as opposed to studied, learned or mastered. I like Michael Meade on genius (and on many other things).
A fish may not be able to be taught to climb a tree unless it’s under water.
You could teach most able-bodied humans to climb a tree, and they could master it if they kept at it for thousands of hours. But some small children are natural climbers – it comes to them naturally and they delight in it. Others take to music. Others to words. Others to painting. Others to invention. Others to building with sand. Others to intuitive understanding of others. Others to prime numbers. Others to philosophy. Or rather, each to their own specific genius, though sadly, most of us to something we forget or never even find, because our parenting, education and culture tend to overlook, suppress, or otherwise fail to notice or appreciate it.
Everyone is a genius, with their own flavors of it; perhaps at more than one thing.
What’s yours?