Hide & Seek works by providing a WebKit Content Blocker extension to the Safari browser on your device. Hide & Seek does not know which web pages you visit, or even which web pages had their cookies blocked because of Hide & Seek.
Hide & Seek prepares a list of rules based on your Hide & Seek configuration, and provides the list to Safari. Safari uses this list of rules while you browse the Internet to determine whether cookies should be blocked on a particular page or not. Hide & Seek is not consulted when you browse the Internet, and therefore, Hide & Seek does not know anything about your browsing activity.
Hide & Seek does not send your Hide & Seek configuration data, or anything else for that matter, to any external server on the Internet.