Quite certain it is not a CGI, doing this good of a CGI would be more expensive than just getting some to fly the helicopter.
The "too stable" comments do not realize that two vehicles filming each other with roughly same speed just look stable.
If you would fake it, the camera would have not done those rotations etc, because that makes CGI much more complex. And there is no faked camera shake/zooms/focus changes that in general happen in all faked videos.
I am using same solution, and getting right count with test input, but the actual input gives too many.
Annoying, and really hard to debug. I made renderer to visualize, but unable to find the bug.
One misunderstanding was that I counted same walls twice, because the result should not count same added wall twice if it has same x,y.