Facebook’s image CDN doesn’t work like this. If I save the media URL and send it to someone, it won’t work for them. I’ve tried — the URLs are user specific.
That's not been my experience playing with this on FB with photos restricted to friends-only viewing. Right-click, open image in new tab, copy that URL and you can view it from an incognito window that has never logged into FB on any account.
Sharing a URL to an asset is different than downloading that asset and sharing it directly.
But this article is about sharing the URL. That’s preventable, which screenshotting is not.