If it washed up on a beach why is it assumed it came from an aircraft or rocket? A ship seems like a far more likely source. Things go overboard, even container

If it washed up on a beach why is it assumed it came from an aircraft or rocket? A ship seems like a far more likely source. Things go overboard, even containers, often enough. I think the better question is, how old is it? And given the ocean currents, where might it have originated?