This is fun!
Not true! If the cabin is airtight, then the air will be traveling at the same rate as the train- thus not moving at all relative to the experiment. Conceptually, dropping a ball at a target in a stationary environment (relative to the surface of the Earth), will result in a hit. Same with an airtight cabin.
With a nod to Leosghost post #3922083 on Heisenburg and cats...
You relativists might as well argue that since you know the precise velocity of the target, you can't possibly know where it will be when the ball is due to hit it. Its simply not the right scale for that argument is to apply.
Of course, if the train was properly sealed, the ball would have both and neither hit and/or missed the target.