Remove Everyone from editing rights

My client wants a particular page to be editable by one user, and for that user to not be able to edit any other content.

I've set up the role and selected that role in the Region Options, but Everyone is set as checked in the 'May be edited by' area on every region by default.

Am I correct in thinking that this would need to be unchecked on every region to stop the role I have created having access to all the content?