The physical analogy is a cover page, intended to conceal the subsequent contents when stacked on a table.

A tooltip change (warning) to the sharing view would be sufficient to address the concerns that the first page is displayed as part of the preview for those with Google Drive integrations enabled.

You should change your tl;dr to reflect that one can view a preview of the first page of a shared Google Doc, despite not having access, when provided the sharing link and with Google Drive integrations enabled.