is one piece episode 821 filler?

In the aftermath of Pedro's explosion in the Chateau courtyard, Count Niwatori gets up, having only received minor injuries. After seeing the remains of the explosion, with no traces of Pedro to be found, Niwatori orders his subordinates to get the wounded to medical attention and put out the fires in the courtyard.

Pedro is alive and with Chopper and Carrot in the Mirro-World. He recalls how the two of them found him through a mirror during his battle, and he immediately hatched a plan to end the fight by detonating the dynamite.