I believe they mean advertised prices, which a menu is (either in your lap or seen from the street). eg, if they have filet mignon on the menu for $30 but then the bill comes and there's a kitchen-appreciation-fee it's not really the fee-for-service that was advertised.

They could also mean they'd like to know if the money even gets to the kitchen, or if the fee itself is kind of a scam where the restaurant is just passing padding margins.