The climax is always the most emotional moment of the story, but also the moment that points towards the resolution. While the resolution does not yet take place, the audience/reader can definitely see an unwinding in the story line begin to take shape.
While the moment that Antigone is led to the tomb is certainly very emotional, the action of the play continues from that point, so the climax occurs further into the play. The climax actually occurs after Tiresias has relayed his prophecy of doom and Creon has finally relented and asked the chorus for advice on what to do. After they advise him to release Antigone, he finally yields and says:
Alas, it is hard, but I give up what my heart wished to do
I bound her and I will go and release her,
for I fear that it is best to keep
the established laws as long as one lives. (1114-15, 1120-23).
When Creon says "the established laws" he is referring to the laws of the gods and finally yielding to Antigone's belief that he should not have passed a decree that attempted to overthrow the gods' authority. However, we soon learn that Creon has changed his mind too late. Soon after this, we learn that Haemon, Antigone, and Creon's wife have all committed suicide, leading us to Creon's devastation and the tragic resolution of the play.
Therefore, the climax of the play is the moment when Creon finally relents and changes his mind, but all too late.
Climax is the most exciting part in the story. For example if A antagonist got killed by a protagonist that would be the climax. Climax is the most dramatic part of the story or play.
The climax is the high point of the story where usually something big happens.