A Classic Flap can be made from anything, Classic Flap is the style, not the material. Classic Flaps are most commonly made from 'Caviar' leather or lambskin.
Caviar is just Chanel's name for a pebble textured, durable leather.
Classic Flaps have been made from Caviar and lambskin-most popular/common, jersey, patent leather, distressed leather, etc . . .
It's not a stupid question, until you're more familiar w/ Chanel it can be confusing.