You have so little time in an interview to learn so much you can't afford to lose the time to both learn whether they can do FizzBuzz (or whatever other problem) and whether they can manipulate some language of interest, when you could be learning both
The purpose of an interview isn't to be abstractly "fair", it's to find the best candidates for the job. You choose what "best" is (which is to say, please don't put words in my mouth about "only interviewing for the exact skillset" or whatever... you choose what is best, whatever that is). My preferred approach is to give the problem, then let the candidate write in whatever language they choose. If they flail in their putatively favorite language with which they've putatively been working for 4 years... well... I've certainly learned some very important things in those few moments.
I thought it was pretty clear based on the second sentence that the comment was intended as a joke. Do I really need to start adding /jk to the end of my comments?
The purpose of an interview isn't to be abstractly "fair", it's to find the best candidates for the job. You choose what "best" is (which is to say, please don't put words in my mouth about "only interviewing for the exact skillset" or whatever... you choose what is best, whatever that is). My preferred approach is to give the problem, then let the candidate write in whatever language they choose. If they flail in their putatively favorite language with which they've putatively been working for 4 years... well... I've certainly learned some very important things in those few moments.