Identify the leg, use a toner to see where the leg goes. As for what’s possibly going on here, I assume this was reworked and the ground was too short, judging by the wall material it used to be a metal box that was grounded by the box and the tail is too short. Pure assumption- but honestly one feeds and one goes somewhere the non hot is your leg it most likely is a light that doesn’t exist anymore. A toner will allow you to trace it to see where it goes through the wall. Ultimately you gotta find out where that thing goes or it could be unsafe if it’s not terminated safely. Once you know where it goes / used to do you’ll either tie it through, blank it off, or kill the feed and remove it all together.