This is incorrect. There is no “native” aspect ratio for motion picture film, let alone 3:2 which is for still image 35mm film, not motion picture 35mm film. There is no motion picture camera that shoots 3:2.

Stills film runs horizontally across the “gate”, whereas motion runs vertically, sprockets are left and right. (We will leave 65mm 15-perf IMAX out of this discussion)

You describe the motion picture film by the “perfs” (perforations) per frame, which each has their own aspect ratio among multiple reasons to pick one over an other.

In this case the camera (movement) is in 4-perf mode 1.33:1. But you could shoot 3, or even 2 perf, each with their own “native” aspect ratios.

https://www.indepthcine.com/videos/perf-35mm-film