is one piece episode 312 filler?

As they sail away from the smoldering ruins of Enies Lobby, Luffy looks all around the Going Merry for Usopp, wondering who sailed the ship to Enies Lobby to rescue them. He's still being fooled by the Sogeking costume; Usopp shrinks behind it, wondering how long it'll be before Luffy and Chopper figure out that he is Usopp.

Sanji tries to get Usopp to admit to the ruse, but he won't. Robin just chuckles knowingly.

Sogeking claims that Usopp sailed ahead to Water 7 in another ship. Zoro wonders how they could possibly not realize it's Usopp.