A dwarf with a preference for a material value things made from that material more than other dwarves would. This includes decorations. It doesn't necessarily mean that a dwarf will be "happy" if they're given items of that material, though. A dwarf with a preference for kaolinite would probably prefer a room made from common flux, for instance, because the preference effective-value multiplier isn't as large as the difference between those materials' material value multiplier.
Kaolinite and porcelain are two different things. A preference for one does nothing related to the working of the other. The preference effective skill bonus is basically just for the things the finished product is made out of. Preferences for rock crystal don't affect crystal glass jobs because they're not making anything of the "rock crystal" material, preferences for cows doesn't help when making cow leather items because those are made from cow leather, not cow, and so on. You're trying to make the system more complicated than it is; the game doesn't "know" what unrefined materials are used to make a refined material, and the things you're discussing involve the game just making things out of the refined material. The unrefined materials - kaolinite, rock crystal, and cows in your examples - aren't considered.
Ash wood and some other materials have an unusual adjective applied to items made of it, so preferences for ash wood affect things made that have that adjective. That's not actually a special case.