5 poster sizes taken automatically from video (external url)

hello, i use external url to insert video in story.
Even though the URL is external, why does the plugin still save the poster, even though I have used the poster from the external URL and in my opinion there is no need to retrieve the poster which is automatically taken from the video.

There are 5 sizes:
*-poster-120×120.jpeg
*-poster-150×150.jpeg
*-poster-150×266.jpeg
*-poster-169×300.jpeg
*-poster-96×96.jpeg
(The poster is saved to hosting storage.)

Is this poster generated from a plugin or WordPress itself? because I deliberately used videos from external URLs to save storage.

Thank You