is attack on titan (shingeki no kyojin) episode 52 filler?

Months ago, during the Struggle for Trost, Reiner Braun and Bertholdt Hoover watched Eren Jaeger prepare to plug the breach in Trost District with a giant boulder. Bertholdt was concerned that Eren would be eaten before the two of them could learn anything about him, and Reiner agreed, saying that if it came to it, he would have to do something with his Titan.

Though Eren's success would undo the work they did to open the hole, Reiner said it would not matter since they finally found a clue after searching for the past five years.