What worries me is that I had done a bit of that previously in the first interview. Some of the people who seemed perfectly able to talk about things in theory

What worries me is that I had done a bit of that previously in the first interview. Some of the people who seemed perfectly able to talk about things in theory wouldn't have passed FizzBuzz. For this position we need people who can actually write code so testing coding ability seemed relevant. Hiring someone who can talk about code but not write a for loop or if statement wouldn't have been a good hire.