is one piece episode 431 filler?

Some of the guards on Level 2 report a massive hole made by Luffy and his party. As they complain that the Sphinx might have fallen down, the Level 2 cells open and the prisoners begin to trudge out.

They move in on the guards filled with vengeance and thank Buggy for freeing them. They send the guards clinging for life.

As the Blugoris are ordered to Level 2, word from Sengoku informs that Luffy and Ace are brothers because of the D. Meanwhile at Marine Headquarters, Sengoku berates Garp over his humor at Luffy's actions.