is attack on titan (shingeki no kyojin) episode 3 filler?

Keith Sadies, the commandant of the 104th Cadet Corps, is psychologically breaking down the new cadets as a rite of passage to break them down so they can rebuild them as soldiers. As an officer and his attendant pass by, they notice Sadies does not subject a few cadets to this abuse and the officer simply notes that their expressions distinguish them from the rest of the group as being present to the fall of Wall Maria two years earlier.

These cadets are shown to be Annie Leonhart, Mikasa Ackermann, Bertholdt Hoover, Eren Jaeger, and Ymir, though Armin Arlelt is ironically not spared.