Can Someone See WhatsApp Contacts if App Downloaded with Their Account?

1)your friends itunes account was probably registered on your phone when you synced with the computer.

2) you can only be synced with one itunes account at a time. your problem might be that your synced with your friends account so any app that you download with your account wont be able to sync any apps unless you change it to sync with your account(which will delete all apps not purchased with your account.)

It was a music file that was bought on iTunes by a friend of someone & passed to me on a memory stick by someone else. For some reason (apparently not a random occurence) when you re-install a back up from iCloud it recognises the original purchaser & asks for their id & password. The app was something random & not connected.