It was a nice demonstration (I'm a big fan of the Spoken Nerd team), but I think the explanation was wrong. The cable was connecting one amplifier to another, and it's a high-impedance input. That means that the high resistance of human bodies isn't a problem - a couple of meg-ohms in series with an input impedance of a hundred meg-ohms or more will make little difference to the signal.
It's also possible that the majority of the conduction was actually reactive rather than resistive (as this was an AC signal) and the signal was passing through the capacitance of the bodies. To establish which was the dominant mechanism you'd need to do a phase measurement between the source and target signals (something we nerds would find quite interesting).