It's a common mistake made in film and television to say a person found dead on their arrival is DOA. But in actuality, DOA means a patient was dead on arrival at the hospital. It goes way back. And originates from the rules that a patient needed to be pronounced by a physician. Today the term still applies to a dead person arriving at a hospital.
Today, with paramedics being given the power to declare a person dead, "Dead on the scene" is used to describe a person found dead outside a hospital. And this is because DOS is classification that denotes a scene that needs a coroner, not a ride in an ambulance.