Unpublished page image visible to Google?

Very new to Grav, but love it!
I've recently created a new website with Grav. For one of the pages that is still being worked on, I've set "Published" to no and the page is indeed not visible when accessing the site. But looking at my webserver logs, I can see that the image googlebot has managed to "view" an image on this unpublished page. How can that be the case?