[Huawei Mate 9 Guides, News, & Discussion] Trixanity:
I know exactly what it looks like hence I stated I thought it didn't make sense to be able to disable it but if you look up what the camera2 API can do then you'll be surprised. I'll pull out the specification for you:

LENS_OPTICAL_STABILIZATION_MODE

Added in API level 21

Key<Integer> LENS_OPTICAL_STABILIZATION_MODE

Sets whether the camera device uses optical image stabilization (OIS) when capturing images.

OIS is used to compensate for motion blur due to small movements of the camera during capture. Unlike digital image stabilization (android.control.videoStabilizationMode), OIS makes use of mechanical elements to stabilize the camera sensor, and thus allows for longer exposure times before camera shake becomes apparent.

Switching between different optical stabilization modes may take several frames to initialize, the camera device will report the current mode in capture result metadata. For example, When "ON" mode is requested, the optical stabilization modes in the first several capture results may still be "OFF", and it will become "ON" when the initialization is done.

If a camera device supports both OIS and digital image stabilization (android.control.videoStabilizationMode), turning both modes on may produce undesirable interaction, so it is recommended not to enable both at the same time.

Not all devices will support OIS; see android.lens.info.availableOpticalStabilization for available controls.

Possible values:

OFF

ON

Available values for this device:

android.lens.info.availableOpticalStabilization

Optional - This value may be null on some devices.

Limited capability - Present on all camera devices that report being at least HARDWARE_LEVEL_LIMITED devices in the android.info.supportedHardwareLevel key

See also:

CONTROL_VIDEO_STABILIZATION_MODE

INFO_SUPPORTED_HARDWARE_LEVEL

LENS_INFO_AVAILABLE_OPTICAL_STABILIZATION

LENS_OPTICAL_STABILIZATION_MODE_OFF

LENS_OPTICAL_STABILIZATION_MODE_ON

So as you can see: the API allows the camera to stop using the OIS to compensate. That would hint that there is a component that engages and disengages the stabilization mechanism. So that would indicate that software can somehow disable the compensation and allow the module to move freely OR allow the camera to disregard the stabilization somehow through some other means. As the specification also indicates: not all implementations allows this but some do. It all depends on your camera implementation. It also seems like it's a good idea to be able to disable OIS if the shot requires it or if you want to rely on heavy EIS which could interfere with OIS (for example to do video recording).

Otherwise you're welcome to explain to me how Google has an API function for something that doesn't work? Seems like that would be nonsense to add it then.

PS. I also just looked up how OIS achieves the compensation and it does rely on a microcontroller and motors. All these can be controlled through software or even just basic electrical circuits, so it would be possible to tell the microcontroller to stop compensating for motion, so it does make sense after all.

Again, you're welcome to contradict this.