The video [https://www.magyaradam.com/wp/?page_id=806] blew my mind. I can only image he reconstructed the video by first reconstructing one frame's worth of slits — then shifting them over by one column and adding the next slit data.

None of the shots in that video are using Slit Scan technique. It’s using a technique called Mean Stack Mode to get the average pixel value across multiple frames, over a rolling selection of an input video.