What portion of the video are you referring to? Give a specific time to look at.
That is a lens-flare effect ... as if there was a strong light-source such as the Sun striking the lens and causing it.
The are called light leaks.
Google light leaks and you will find some free ones.
Great demo, Paul ... spiffy to use a tiny frame-size, blown up and blurred ... I can see other uses for that idea ... 😉
Using the Noise HLS Auto effect as a Fractal Noise opens up the possibility for all kinds of effects.
I see what you mean!
One of the really cool late-50's movie/TV credits screens was a sort of silky-glowing cloth semi out of focus as the background. I've seen other things for setting up something like that, but they all included using a plugin or actual video clip.
Noise HLS as you used it here should be able to do exactly the same thing. Easily, quickly, and it seems with very little stress on the machine. Awesome!