is one piece episode 601 filler?

Caesar Clown and the children are seen disembarking from the Flying Gas Balloon, surprising the nearby Marines and they question what the ship is. Entering the research laboratory through an upper entrance, Caesar reminds the children that the lab is their home and their candy is in the Biscuits Room.

He then orders his subordinates to lock the doors and to make sure they do not escape again. As all of the children hurry inside eagerly, Mocha, who upon entering the room, begins to resist the addictive drug and remembers her frightening memories of the lab.