I'm assuming it was a 747-400 here..
The seat wiring runs from seat to seat, then to a disconnect at the wall where it interfaces with various boxes that do different things, like pax lights, hostie call, IFE etc. its possible that the whole system went haywire and assigned the wrong "address" to each seat, therefore switching on the wrong light when the button was pushed. It's been a few years since i worked on these, so please forgive any errors. It's usually solved by doing a master reboot on the system.. i haven't heard of all zones being affected before though, usually it's a problem with the one group of seats that are hooked together (typically around 8 or so). Maybe the hostie dislodged the PSUD controller from the lav with her heel?
