The tongue twister was a dead giveaway. Personally, I'd walk out (or hang up) as soon as the Oxford Comma came up, but I have less patience than most.
Anyway this article has a point that this process isn't effective for finding good writers, but I'll be damned if asking people to write one or two sentences doesn't filter out the illiterate people that wander in your door (think FizzBuzz).
It's irrelevant trivia. All you're going to do is trip up people who may not have been exposed to the terminology or hadn't encountered both styles yet. Any writer can handle either style and knowing the terms says nothing about whether someone can write.
FizzBuzz is about making sure someone has a basic handle on the actual job. An equivalent for writers would be to ask for a quick poem or three sentence story or something.