That was likely the thought process of the interviewers, however wrong.
FizzBuzz works well enough as a lowest common denominator screening test, but it doesn't scale up. At its core, it's an entirely made up problem with no relevance to anything you may ever do at a job. How do you evaluate requirements for a problem that is not real?
The higher level the skills you want to test, the more realistic your questions have to get.
A real job is often simialar to fizzbuzz in that there is no eligant solutians. There are several solutions but they all have some special case. a real world problem would take you a week to solve though and so we can't give them to you in an hour.
FizzBuzz works well enough as a lowest common denominator screening test, but it doesn't scale up. At its core, it's an entirely made up problem with no relevance to anything you may ever do at a job. How do you evaluate requirements for a problem that is not real?
The higher level the skills you want to test, the more realistic your questions have to get.