If I insert an image to a WordPress docuament via "Add Media -> Insert from URL", and after submitting the URL and inserting to my post, is the image linked to my page or copied to my site?
If you use "Insert by URL" the image is loaded from whatever URL your provide. It is not uploaded to your server at all, nor is any information added to the
You can pretty much work this out by looking at the page source, but I also tried to search the database of evidence just in case. I did not find any.