does it mean all previews are sent from FB server? Or the link is embedded from the source?
When you share a page on social media, the platform (in this case Facebook) pulls in certain information from the embedded webpage, including the title, author information, page summary, and often an image. More information can be specified in the html header in meta tags. See this link for more information on meta tags: https://moz.com/blog/meta-data-templates-123
If the preview is from the link source, then will it reveal user that viewing a page on FB to the source link?