bought an iPhone 5 it ask to login with different account after restore

I bought an unlocked iPhone 5 in UK, I had an iPhone 4s.

I restore my iPhone using iCloud: everything was fine, but after the restore the iPhone asked me to login with a differnt account (a different email... which I've never had!).

I clicked "cancel" and now everything works fine, but I don't know what to think about: was my iPhone already bought (and then sold) from another one?

Is it normal?

I've no problem with my new iPhone, but I'd like to know why it did this.

Thanks!