Ditching the aircraft means they've been shot down or rendered combat ineffective.
Actually, ditching merely means that a player didn't land their aircraft on the runway or designated landing area (whether someone else caused that player to or the player just did it). There is no consideration of why .... only that the player didn't die (or bail). To be honest, I half expected this thread to be a satire (though it's even funnier if it's an attempt at a 'serious' debate).
But .... how the hell would ya code the game to know that a plane that took hits then ditched was a kill? (No, really, think about it.)