[EasySt]

Sorry, but that IS real lightning.

The camera is in portrait mode, so the sensor scan is oriented vertically.
As the low intensity lighting "feelers" come down, the image is not overexposed.

Once the path to ground completes, the power comes through and the over
exposure begins in that instant, mid frame scan. In your video at that link you can see the streamer that "connected" heading in from the right:

In the video the scan is capturing the image by scanning from the right to the left, instead of top to bottom. That makes the main flash look like an overexposed vertical bar.

I actually captured and shared elsewhere a similar effect from our last Reno storm.
Here, the camera is in landscape mode and the frame scan is horizontal. (Filling in from top to bottom.)
note the streamers at the top of the image.

(I was recording it in real time.)

#wwg1wga

[Ymani Cricket]

interesting. Ive never had that happen while videoing lightning storms. But I didn’t use landscape mode and I think 35mm is way more fun.

[EasySt]

Actually, the streamers in my image are not quite at the top of the image,
because they had not yet begun when that frame scan did.

About the same distance down, a streamer or streamers connect, and the
overexposure happens.

Knowing all the specs and settings of that camera, quite a bit of science
could be extracted from that one frame of my video, alone.

~Easy