Yeah, this arc premiered in theaters. I didn't go, but after watching the first two episodes it really felt like it was basically a bait and switch. The first episode starts off with a very cinematic animation style but after the intro it reverts back to TV animation.

It was basically a reverse Mugen Train, which itself was a weird decision. They thought the arc was too short for a season so they made it into a movie, but then decided to adapt it as the first part of season 2 anyways. They basically cut the movie into episode chunks, and you can tell because the animation changes in the episode after the movie adaptation ends.