It’s not a video link, it is an html page the link of whivh ends in .mp4.
To the browser, apps, (and most things really), file extensions are just text, the file type is inferred or for http sent with the server response as a mime type.

In any case, this html indeed can’t be played as a video. Try the direct catbox link:
https://files.catbox.moe/qs59yx.mp4