I think the algorithm in the video is doing a very specific thing where there's a zero-width pixel-grid-clamped stroke (picture an etch-a-sketch-like seam carving "between" the bounds of pixels on the grid) moving about the grid, altering (with XOR?) anything it advances across.

So, sure, you could try to implement this by having a seam that is made to "reverberate" back and forth "across" the outlining pixels of a static shape on each frame. But that's not exactly the same thing as selecting the outline of the shape itself and having those pixels update each frame. Given the way this algorithm looks to work, pushing the seam "inwards" vs "outwards" across the same set of pixels forming the outline might gather an entirely different subset of pixels, creating a lot of holes or perhaps double-counting pixels.

And if you fix those problems, then you're not really using this algorithm any more; you're just doing the much-more-boring thing of taking a list of pixel positions forming the outline and updating them each frame. :)

I believe the algorithm in the video works by flipping the pixel color when the pixel changes from foreground (some shape) to background, or from background to foreground. If the shape doesn't move, there is no such change, so it disappears.

In the OP the foreground pixels continuously change (scrolling in this case) while the background doesn't change. That's a different method of separating background and foreground.