Secret room?

I don't know what is going on with this secret room I found one day. I was expanding my basement when I found this room just underground in the middle of nowhere. It had a dirt block, a crafting table, a furnace, and a chest with nothing in it when. I went onto the same seed (-1200 also on an old world) and dug in the the same exact place trying to find a room it wasn't there I have tried this three or four times and it's only on that one world. I don't know if this is a bug or not but if you could check it out though very helpful. I don't have any idea what is going on. it's Been here for a very long time . It is not a dungeon. I don't know someone was just trying to prank me or its something bigger .