A touch screen calibration error would result likely in being off a few pixels or so - not inches or half-inches like ballot choices are separated. To get that far off it would seem to me the miscalibration would have to be INTENTIONAL.
I have worked with several types of these machines This happened twice. The first was a man whose hand was shaking so bad that he kept hitting the wrong button. Solution -use the visually impaired screen where the buttons were far apart. The other time was a woman with very long fingernails. She aimed her finger tip at the correct spot, but her nail hit the spot above. I watched her do this and had her be careful.