is attack on titan (shingeki no kyojin) episode 55 filler?

Eren Jaeger stands momentarily speechless over the burned body of his childhood friend, Armin Arlelt. He realizes he should have known what would happen, but had no choice but to rely on him.

Eren hears the weight of a Titan landing in the distance, and turns around in time to see the Cart Titan, carrying Zeke on its back. The Cart Titan gallops across the rooftops to reach Eren, who quickly moves to hold the unconscious Bertholdt Hoover hostage, placing his blade at the Warrior's throat.