Tl;dr : from both this article and from Anders Ericksons himself, the key isn’t “it takes 10k hours to be a master”, it’s “there are no masters who didn’t dedicate 10k hours to get there.” These are not the same.
The difference, as Ericsson explains in his book Peak: Secrets From The New Science of Expertise, is that 10k hours of bad practice won’t get you there. The masters practiced effectively to get there.