I still see your point. However, how do you solve a problem if you just don't know something? To me, a big factor in this test is, did they finish and does it work? Lets say they understand that Modulo would be the way to go but they are unsure of the syntax. Where would they find the answer? Or do we say, sorry you're out...you must memorize everything?
Being able to look up information on demand is an important skill, but that is not what is being tested by FizzBuzz. Furthermore, if it is a skill that needs to be exercised while attempting FizzBuzz, that is a disqualifier.
'FizzBuzz without Google' doesn't mean the candidate is expected to have memorized everything. Just a very minimal baseline.
You can always test Google-skills separately, if you think it is in doubt.