is attack on titan (shingeki no kyojin) episode 26 filler?

For just over a hundred years, humanity lived in peaceful ignorance within the Walls safe from the threat of the Titans until the day the Colossal and Armored Titans came to Shiganshina District, breaching Wall Maria and reminding humanity of the hell beyond the Walls. Five years later, humanity discovers that some of their Titan foes are hiding among them as humans, and in Stohess District they capture the first of these Titan spies: Annie Leonhart.