Does the author claim this isn't something you can train for?
I've given hundreds of coding interviews. I always timed the candidate (with their knowledge). So I have a general idea of the distribution of programming speed, and my guess for this particular problem is to solve it in 10 minutes, you need both talent and practice... just one isn't enough. So asking people to solve it in 10 minutes ends up filtering out untalented people who have practiced a lot (and talented people who haven't practiced as much)
I've given hundreds of coding interviews. I always timed the candidate (with their knowledge). So I have a general idea of the distribution of programming speed, and my guess for this particular problem is to solve it in 10 minutes, you need both talent and practice... just one isn't enough. So asking people to solve it in 10 minutes ends up filtering out untalented people who have practiced a lot (and talented people who haven't practiced as much)