I found this, an excerpt from a transcript:  Rory: We’re fondue purists, Grandma. Lorelai: Yea we dip old school. Emily: The government says you should have nine servings of fruits and vegetables per day. Lorelai: Imperialist propaganda. Rory: Noam Chomsky would agree. Lorelai: I bet Noam doesn’t dip fruit  (gilmore girls) "The Gilmore Girls" was an American comedy series that ran from 2000 to 2007. That dialogue is typical of a parody of the conversations of sophisticated urbanites. With context, we can now comment on this dialogue. A fondue purist is one who sticks to the Swiss original of cheese and bread. No fruits. "Old school" means "traditional" - just cheese and bread. So they are echoing each other.

I think that the use of the term "fondue purist" is an attempt at humor. It is certainly hyperbole, by suggesting that the granddaughter ONLY eats fruit when dipped in chocolate or other tasty (hot melted) sauces. While I have eaten fondue as a child, I have never heard the term used.