The slides mention that the video on Youtube shorts is a screen recording of TikTok.

It's likely that the TikTok video was simply downloaded using the download button, no trickery required. In contrast to Instagram and Google's walled gardens, TikToks videos are easily shareable and so often end up being uploaded onto these platforms[0] - with the branded watermark leading viewers back to the original source.

Part of the reason for their success I think.

[0] https://www.socialmediatoday.com/news/instagram-will-now-lim...