Hey, sorry, it took this long to answer. I’ve missed this thread totally!

The most likely answer for both of you is an electrical arc (current jumping across a small gap through the air). It builds up when two materials touch and electrons move from one to the other. But if there was a thunderstorm around, my bet is that the lightning energy got into the building through its wiring (or its pipes or metal conduits) inside its walls. Static and ball lightning are both possible too but rare.

Lightning doesn’t have to hit your building to get inside. It can come thru wires or pipes that run outside, or the ground. Once inside, it travels along the electrical, phone, plumbing, and TV systems, and along metal wires or bars in concrete walls and floors. So a spark next to a computer during a storm fits this well. And “no wiring near that location” only covers the wiring you can see. Cables and metal run inside walls and roofs too (I hope you both had it checked with an electrician. Again, sorry for the delayed response!).

During a storm, the US National Weather Service (NWS) says to stay off corded phones and away from computers, cords, and plumbing. A typical surge protector won’t protect your gear from a lightning strike, and you shouldn’t unplug things mid-storm either, as you could be struck while doing it.

But whatever it was, I hope you got an electrician to look at that spot.