Mostly correct. Most non-alcoholic beverages at more DP restaurants are included. That often includes shakes and smoothies, but not always. It does not typically include anything served in a souveneir cup.
Non-Disney owned participating restaurants are a bit more strict -- they may limit the beverages to sodas, regular coffee, etc. They may exclude shakes, specialty coffees, etc. But Disney-owned restarants are usually more inclusive.