Typically this is explained by the saying, "current kills."
It's not the charge (or potential above ground) that a body attains that hurts biological systems, it's the current that flows through them and either 1) heats them or 2) disrupts important electrical signals in the body.
Heating damage occurs and can "cook" (cause 1st, 2nd, or 3rd degree burns internally or externally) portions of the body where the current flows.
Electrical disruption is the more deadly of the two, commonly. The heart depends on regular electrical pulses from the sinoatrial node to contract not just rhythmically, but for the entire heart to contract at the same time. If an electrical current is induced across the heart at the wrong time, or across a weak heart it may lead to atrial fibrillation. This is the most common abnormal heartbeat pattern the heart ends up following when presented with such an electrical interruption, and it's extraordinarily inefficient, leading to low blood oxygen. AED (automatic external defibrillators) are designed to detect this abnormal beat, then apply a specific electrical current and waveform to the heart to give it a good chance of regaining normal beating. With very high voltages, we can discuss the muscle contraction that takes place, and the possibility that this would cause the person some damage depending on their location (ie, throwing themselves backward into a concrete wall due to a sudden jolt), but this wouldn't be the case for the situation at hand.
While heating does occur any time there's any current flow (except in a superconductor, theoretically), it takes a lot of current to cook organic materials.
While the heart can react to electrical currents, it's not very sensitive.
Thus it's the current that flows through the body, or the heart in the case of fibrillation, that is important.
The charge required to bring a human body up to the potential of the circuit they are touching is very, very small. Effectively the human and ground becomes a capacitor with an insulator between them - a small one on the feet, and the air as insulator elsewhere. The capacitance would be very small as the insulator is neither thin nor large (the closer the two conducting surfaces, and the larger the surfaces, the greater the capacitance).
So it would only take a very small amount of current to charge up the body, and that current isn't significant enough to cause either heating or electrical signal disruption.
Further, from the point of contact, the charge would rapidly radiate throughout the relatively conductive body, meaning that the area of greatest current is the contact point, but after that no other spot on the body receives any significant amount of current. Even if you were able to increase the capacitance significantly, and you chose a very, very high voltage, thus forcing many more electrons into the body, the only part that would become damaged would be the heating damage at the point of contact with the conductor providing the charge. You might get a small electrical burn there.
So the situation you describe could only generate a very, very small current to bring the body up to a specific voltage potential, and thus would be unlikely to produce any damage.
That being said, don't do it anyway. Take all reasonable precautions.
If the circuit used alternate current, it might happen that a wrong terminal would introduce additional series capacitance or inductance; these could cause the breaker trip if the original load was mostly inductive or capacitive respectively. But it is not probable that the effect of a termination would be sufficient for this.
Instead I conjecture that there was an internal capacitor in the load. After losing its voltage during a short power breakage at the faulty terminal, it would have recharged too fast, causing a transient current surge.
The connection at the wrong terminal could be re-established just from a random mechanical reason, or could even occur due to negative differential resistance of some oxide layer.
Best Answer
To start with one could have an ac current never grounded anywhere , for a household generator for example. The reason one grounds at the generator is for safety so the ground can pick up any miss chance, as it is a practically infinite sink for electrons. Only one of the two lines can be grounded of course :).
It was found though that due to capacitences the ac neutral even though it starts with zero at the ground ends up in households with some voltage difference dependingon the distances traveled from the last grounding of the supply circuit. I have measured up to 45 volts to the ground difference on the neutral in the 220 we have here.
The household is grounded to some water pipes etc for the same reason it starts grounded, so the outside of appliances is safe for the casual user from small accidents.
Sure, due to the infinite sink for electrons of the earth of course the circuit will close to the ground whether the short circuit was from the neutral ( floating) or the live, both would be live in this hypothesis. Grounding at the factory/generator is for safety of use, reduces probabilities of fatal accidents, and in order to assure a stable voltage difference to the user, not floating where then the accidental shorts would be more dangerous. As it arrives floating a bit by the effective circuit the current traverses to the homes, houses have to be grounded again for safety reasons. Having one of the two wires close to ground voltage reduces probabilities of accident by 1/2