Interviews are lossy compression of a career, experience, and brain shape, over a noisy channel of whiteboards and human speech. The best you can hope is that your interviewer will recognize the larger pattern.
BUT. There is limited time in an interview, so we try to scry nuances like a soothsayer with a pile of sheep guts. Every detail gets magnified.
Examples:
"You chose to return an error code instead of throwing an exception." Is this an optimization, or have you spent a lot of time on system programming?
"I see a couple of fenceposting errors." Is it nerves or do you not have the right shape of the problem in your head?
"You passed some bookkeeping information in a recursive call that should take care of itself." Do you not understand recursion, or are you misremembering something cool about accumulators and tail recursion?
"You chose to use inheritance instead of composition." Have you ever had to extend or maintain such a design, or did you read about it in a book?
"You used template metaprogramming." Are you a misunderstood genius or do you delight in writing unmaintainable constructs from the dark corners of C++ into production?
"You chose to use Perl but don't know what a hash is." Do you have any questions for me?