It’s 4kb it’s the demo scene.
To expand, the rendered to video output is much more than 4k, but the file that produces the output can be small like that, this is usually done by doing a bunch of math to generate the output dynamically.
You can kind of equate it to how a video game can generate 120 frames of 4k footage every second indefinitely, but the game itself is limited in size.
Recording the output takes up space, but you don’t need to record it if you can generate it in demand.
I agree, functional programming is the future