I think you’ll find the interior is “stoneware ceramic”, which is a mix of clay and silica, fired to a high temperature with a heavy red glaze. Relatively modern.
Although popularly nicknamed the “Laughing/Fat Buddha”, the representation is not actually of Buddha. It’s “Budai”, also known as “Hotei”… the god of fortune, guardian of children, patron of diviners and barmen, and also the god of popularity. His name translates as “cloth sack”. Note that he’s carrying a sack over his shoulder which is historically said to be loaded with fortunes for those who believe in his virtues, although in Chinese he’s also nicknamed “Cho-Tei-Shi” or “Ho-Tei-Shi, which means “bag of old clothes”.
He was a semi-historical itinerant Chinese Zen priest/monk with a recorded death in March 916 AD who has become amalgamated with a pre-Zen Buddhism Japanese manifestation of Miroku… the patron of those who could not be saved by the beliefs of Buddha.
