I agree with you that if someone is spending forty hours a week writing code at work, it makes no sense to expect him to write more code in his spare time. That's the bad part of the article.

The good part of the article stands, though. In a good programmer, there will be a spark, and he has the right idea about the interview question.

A perfectly valid way to respond to it would be to refer to something you did at work. "Oh boy, that's difficult because the code I've had to deal with has been legacy stuff that... well let me see, there was this big ball of mud where it took us a week to track down an intermittent bug, the debugger was useless... but after that, I figured out a way to put in logging code so we could at least see what was going on and we'd have a better chance next time..."

You're not looking for spare time programming or some particular answer. You're looking for a non-rote answer. You're looking for the spark.