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If who ever it was that took your phone viewed the information and then wrote it down on paper or took camera photos of your screens, there's no way for you to know.
I encourage you to read the below linked article, never give out your passcode, and take better advantage of the security features that your iPhone offers.
Six ways to increase your iPhone and iPad security in 2016! | iMore
The next time your iPhone is stolen, use these features to wipe the information from your phone:
https://support.apple.com/en-us/HT201472