For others interested in why ray tracing scales O(log N), this is covered in an earlier video in the NVIDIA "Ray Tracing Essentials" series, specifically this one:
https://youtu.be/ynCxnR1i0QY?t=173
It's timestamped to the discussion of why this is true, but the whole video (like the series, IMO) is very informative, this one focused on "Rasterization vs Ray Tracing".