is attack on titan (shingeki no kyojin) episode 1 filler?

The giant hand of a Titan above Wall Maria, humanity's outermost Wall, ominously looms over the onlookers below, gaping in awe. The narrator explains how on that day, humanity received a grim reminder, and how they lived in fear of the Titans and were disgraced to live in the cages they called Walls.

Earlier that day, beyond the Walls, the Scout Regiment are traveling through a forest when they encounter a Titan. The soldiers attempt to assault it in an effort to establish humanity's first base outside their own Walls.