I found it when searching how to make gifs in Linux.

So, the files there

at least some, if not all

are WebP, not GIF. Which is probably generally desirable, as for most content, WebP is going to provide better compression and visual quality.

(I'm assuming that you're talking about animated video files.)

EDIT: Actually, WebM would probably be preferable to WebP for video.

goes to benchmark a video snippet

$ yt-dlp 'https://www.youtube.com/watch?v=_5lENnRGei8&pp=ygUJc3VycHJpc2Vk'
$ ffmpeg -i Boy\ Surprises\ Childhood\ Best\ Friend\ Dressed\ As\ FedEx\ Driver\ \[_5lENnRGei8\].mkv out.webm
$ ffmpeg -i Boy\ Surprises\ Childhood\ Best\ Friend\ Dressed\ As\ FedEx\ Driver\ \[_5lENnRGei8\].mkv out.webp
$ ffmpeg -i Boy\ Surprises\ Childhood\ Best\ Friend\ Dressed\ As\ FedEx\ Driver\ \[_5lENnRGei8\].mkv out.gif
$ ls -Ss1h out.*
497M out.gif
 95M out.webp
 18M out.webm
$