Huh? My place has similar rite. People send food to the sea for a sense of gratitude. Sometime if you being cursed or found a curse talisman, you either burn it or send it down the river. If you wanna curse someone with love curse, there's a way you can do by sending several object including target photo into the sea.
In some extreme case, people who did too many sins they rejected by the earth, they send down the deceased on the river.
It's quite amusing seeing two different civilizations separated by sea share similar rite.