I don't know who that quote is from, or which thread, but maybe ask them for the code reference?
AFAIK, you're right. Or would be, in NY.
The requirement for bathroom ventilation is in R303.3 - says you need an openable window, or a fan (20 cfm if constant, or 50cfm if intermittent). But it doesn't say anything about having to be on the same switch as the light. Not only that - in NY, the energy codes say it has to be on a separate switch.