According to Tiresias, Creon has hurt Thebes by engaging in behavior that threatens to bring down the curses of the gods upon the city.
This is all because the stubborn Creon has refused to allow Antigone to bury her dead brother Polynices in accordance with the established burial rites. Instead, the king has allowed the young man's corpse to rot in the street, as he regards him as having been a traitor against Thebes.
In this particular scene, Creon starts by vowing to Tiresias that he will obey whatever advice he gives him. But when the blind prophet tells Creon in no uncertain terms that his refusal to allow Antigone to bury her brother will bring down terrible curses on Thebes, Creon changes his tune and refuses to accept what Tiresias says.
Infuriated by Tiresias's prophecy, Creon accuses him of being a false prophet guilty of poor advice and bad rhetoric. But Tiresias has a deep understanding of what the gods want and so is not about to back down. He knows that burial rites are the sole concern of the gods, and it's therefore impious for any mere mortal to try and interfere with them as Creon has done.
Tiresias stands his ground, and a worried Creon reluctantly agrees with the will of the community, as represented by the Chorus, to free Antigone from her captivity.