An acquaintance of mine (sister's bf) has 2 iPhones, work and personal. He says his work iPhone contacts were transferred to his personal iPhone without any user interaction.Contact information is not shared automatically, and it is a user-initiated process that requires both people exchanging information to accept the transfer. While an accidental exchange could occur, it would require a user to unlock their device and accept the sharing prompt for that to occur.
Unfortunately I don't have the details at this time, like exact iPhone models and versions of iOS.
I realize this sounds fishy, and I would think we'd have more people coming forward, considering there are probably a lot of people with work / personal iPhones.