The other problem is that newer power supplies tend to be of the switch-mode type; these rely on "chopping" the input (often with a local increase in frequency) and then smoothing it off, this means that as current levels change it is necessary to adjust the amount of chopping required based on monitoring the output voltage. Sometimes, there are no inductors involved, let alone a transformer - merely capacitors. Such power supplies have an additional advantage of being small and highly efficient. Therefore they are desirable for non-pecuniary engineering reasons.
A plausible scenario is:
Slight water leakage into phone/charger socket interface, voltage appears to drop, power supply overcompensates sending a short burst of high voltage through. This causes a brief electrical shock, possibly (or not) enough to kill but opening a passage through the body for the electricity. Further damage occurs as lower voltage (but higher amps) pass through the body.
Another issue is that phones may use other types of circuit to drive from a battery whose nominal voltage is lower than the circuitry. This could also end up "pumping" more electrical charge and energy through. A second, complimentary scenario based on this pumping effect is that electrical energy leaked back from the phone battery and contributed to the damage, particularly the extensive burns. It is quite possible to get internal burns as well.
A third issue would be that a surge as described above may cause "contractures", which are involuntary movements provoked by such electrical activity and means that someone is left holding onto the power source despite their best efforts otherwise. It may account for the deceased having burns to his hand.
