This is probably far fetched but stay with me now. We have all seen the newest episode of Arrow (and if you haven't what is wrong with you) anyways so they cant kill off one of the main characters aka Felicity. So i think it could be some one else. Remember Oliver Queen had a kid. He thinks he/she died. He also ran into the mother in central city. So she might get back in touch with Oliver and tell him the child is still alive. The child would be 7 years by now. It has also been 6 months since he came back to star city, he could of connected with his child. Plus, the grave is a little short looking. Again, this is just a theory. What do you think?