This type of fault is not rare. Many times the ground systems of audio and other equipment are at different potentials, so by completing the circuit, a current flows. Sometimes through a human! Many foreign countries don't have the same grounding principles as the U.S., not that they're bad or flawed, but the danger comes in mixing equipment from different areas and not modifying them to meet local standards. I cannot say if this was the case here, but I have read documented cases of audio equipment in recording studios doing similar things. Such as a singer strumming his guitar and touching his lips to a microphone that is at a different potential. The metal strings are grounded through the guitar amp, and bam, a ground loop is established and zing, a shock!