I liked this episode! The preview only showed Ash and his group roaming around the rocky area, showing Ishizumai here and there - so I thought the episode would be boring. Also, I had a feeling Dento would get the Ishizumai because he was shown a lot so that was pretty interesting. From the preview, I thought it would be a boring filler. While watching the actual episode, it showed Team Rocket AND Ishizumai's bonding time with Dento so this episode turned out to be great.
To me, it doesn't seem like a filler. I'm glad Dento has an Ishizumai now. I'm expecting it to be extra caring for the group, mainly Yanappu.