Correct. I wouldn't even call it Sandbox. It simply boils down to having a more open level than the rest. People don't see to get that.
Just having a slightly more open level design does not make a game OPEN WORLD. Open world is Fallout 3/NV, TeS and a few other games that don't do it as well.
TLOU isn't even sandbox. Sandbox would be ArmA or similar games where you have this large world, but you have to make things to do in it.