I saw that happen in a game where I deleted the tombstones of dead sims. (At the time I was acting on erroneous advice that it would stop lag, but little did I know that it could actually make it worse or cause corruption.) I think the technical explanation if it isn't a living sim is that it's a "mini-sim" in the game, which is how the game renders foreign sims when they're not in your world. If I understand it correctly, the game doesn't realize that sim is a ghost or dead, and is storing just basic information about the sim because there is a tie to sims in the world.