Well if the current (I) is really big, and you say the voltage (V) is very low, that means resistance ® is even lower. At 20 million amps, R would need to be really really small for the voltage to also be very low.
They put the 20 million amps basically through a tuna can, which I would think would have a resistance would at least be 0.01 ohms, putting the voltage at 200,000 volts!!!!