is one piece episode 19 filler?

After Luffy finds a box of cannonballs onboard, he and Usopp decide to play with the ship's cannons. As they do so, Zoro takes a nap, where he dreams about his childhood.

Zoro was a dojoyaburi at Shimotsuki Village, challenging local dojos to duels. However, after challenging the dojo of Koushirou, he faced defeat at the hands of Koushirou's daughter, Kuina, and as promised had to join the dojo as a student.

After training much more rigorously than his peers, he became strong enough to defeat the adults at the dojo, but was still unable to defeat Kuina.