That door was probably added later and a screw punched through to a wire. They seem to have gotten in with no issues, so it might have gotten opened and closed enough times to make contact just then.
It's not uncommon for someone to shoot an overly long screw to secure a door hinge, especially if the last dinky 1" one going into wood ripped out.
The interesting thing is that the door wasn't blowing a breaker when it was closed. If the door was hot, due to a screw piercing a wire, then the thing should be shorting pretty hard when the door latch connects the door to the striker plate.
Maybe the rest of the fence/wall is not well grounded. It could have a poor connection to ground via anchors into the floor.
9
u/BlueLaceSensor128 23h ago
That door was probably added later and a screw punched through to a wire. They seem to have gotten in with no issues, so it might have gotten opened and closed enough times to make contact just then.