NHUK
New member
https://dev.windowsphone.com/en-US/OEM/docs/Driver_Components/USB
All the info is in the link above, from what I understand, it presents a prompt when the user connects the phone to a computer asking whether to allow access to the internal storage. The 'data connection' refers to access to internal storage. It seems though from the webpage that phones updated from wp8 won't have this feature.
I have to say, that was my guess. In the olden days whenever you plugged in a phone to a computer it used to ask whether you wanted to enable data connection (or ovsuite, or whatever your software was at the time). This was so that you could just plug your phone in to your PC to charge and nowt else. I don't think its any more cleverer than that