This is their fault, if it was fake, for buying shitty pink USB chargers...from China, but then again outside of Bigclive how many PSAs are there warning about those things? They are even dumber if they don't have any sort of RCD in the bathroom such as an in-socket GFCI or one one the whole circuit. However, it could have failed, most people don't test them. It could also have been a total ground failure to the house and current flowed back through neutral, if they had a shitty cheap breaker too, reverse current may not have tripped it.