Honestly, it was a pretty quiet episode. It didn't push the restaurant plot forward or give us any deep character development, so I'd definitely consider it a total filler episode. It was nice to see everyone hanging out, but honestly, you could completely skip this episode and it wouldn't change a thing regarding the story. By the way, it's the most elegant 9-year-old's birthday party I've ever seen in my entire life watching anime, lol.