It would initially have the same speed as the train, and to the 'train dropper' seem to fall 'straight down' ignoring all resistance now. Same as inside the carriage in fact

From a stationary observer watching the train pass, it would move in a arc, now assuming that the train doesn't have a velocity allowing the ball to reach orbital speed. If you include air resistance it will also slow down relative both observers, and as you say move backwards from the train droppers POV. Assuming that the 'train dropper' defines the train as stationary he will now be in need of a strong drink to cool his nerves as everything moves the wrong way

I think?