People sometimes leave their site logs public, which I suspect means google could find links to private pages in the referer logs.
(Of course, people should be relying on more than obscurity to hide their private pages! - but I believe people have been known to make mistakes and/or not know what they're doing.)
(Of course, people should be relying on more than obscurity to hide their private pages! - but I believe people have been known to make mistakes and/or not know what they're doing.)