The OP said that one should know how to write a fizzbuzz. I said I couldn't cause I don't know what it is. That doesn't mean I couldn't once it was explained to me.
My point is that they clearly didn't mean you should be able to write one from hearing the word fizzbuzz. It's used by name online because it's fairly widely known around these parts. In an interview question it would be given to you as a set of requirements, not just the word fizzbuzz.