So it is written in Wikipedia. This is a popular dish and cooking process in Philippine cuisine that involves meat, seafood, or vegetables marinated in vinegar, soy sauce, and garlic, which is browned in oil, and simmered in the marinade. It has sometimes been considered as the unofficial national dish in the Philippines.
Although it has a name taken from Spanish, the cooking method is indigenous to the Philippines. Early Filipinos cooked their food normally by roasting, steaming or boiling methods. To keep it fresh longer, food was often cooked by immersion in vinegar and salt. Thus, it is very likely that Filipinos could have been cooking meat in vinegar as a means of preservation. This process dates back to the Classical Period and was used for pork and chicken