Software engineers are given problems to solve, and their job is to solve these problems efficiently. You don't always have the solution to every problem off of the top of your head. That's why programmers use Google, StackOverflow, and documentation as resources. The primary skill employers are looking for is learning how to learn new things quickly. And I believe I demonstrated that skill in my interview.
Also, I declined to mention this in the article, but after I finished that UTF encoding problem in my interview, the interviewer asked where I got the check-bit macro (he saw me paste it in). I told him I got it from StackOverflow. It didn't seem to concern him.