is one piece episode 391 filler?

At Grove 41, Franky and Usopp fill up with some cola with Sanji also staying on the Thousand Sunny. He plans to wait for Nami while guarding her treasure.

Zoro disembarks and heads to town. Zoro yells out that the trees are marked by numbers, so he won't get lost.

He first thinks the grove is number 1, due to a bubble blocking the first digit. Meanwhile, Hatchan explains that the World Nobles are also known as the Celestial Dragons and wear masks, so they don't breathe the same air as common people.