In Confluence, the user does have the ability to share pages to the emails of non-existing Confluence users. When sharing the page, the same will receive the notification to see/edit the page. However, if the user does not have an account in the application, the same will be prompted with a message to use a different account in order to log in, since the same does not exist. 

The user will be only able to see/edit the page if the same has the permissions opened for anonymous. This is a suggestion to send an invite to the non-Confluence user in order to be able to join the application and edit the page.