It was someone's hackery. That's not an OEM ground wire.
You should do your best to inspect the cabin, trunk & engine bay for more hack work.
I found multiple live 12v wires under my center console, just waiting for the right pothole to light my car on fire, all over the cabin/trunk.
Can't stand when people mess with electrical harnesses, they almost never splice or secure them properly.. wire nuts, electrical tape, exposed butt-connectors.. Lord help me.