I've had the car since September 2018 and such avoidance only happened once (a few weeks into ownership) so not really surprising at all to me.
It'd require:
Something that's only happened once in over 6 months to happen during the 1 month side cameras have been online
AND
It happens to someone running dashcam
AND
That someone doesn't have a repeated camera file failure as many seem to have
AND
That someone is on the forums and cares enough to find the thread and post the video
I guess I'm not sure what you are "skeptical" of?
Side collision avoidance is a known, explicitly listed, feature of the car. It absolutely exists and works, there's numerous reports of folks, myself included, having had it happen to them.
FWIW, there ARE videos of it out there- quite a few in fact. Just none that fit ALL the criteria I listed.
Watch Tesla Model 3 Autopilot Avoid Dangerous Side Collision: Video
That's one with only the front camera, and not posted in this thread.
here's a Model S doing it- again front camera only