If I understand correctly, neither.
OP, was it something like this box:
Image
If so, the email address is filled in based on the content it's trying to authorize. It means that something it was trying to access was originally purchased with whatever account you saw there, instead of your own. Did you copy some music or other content from a friend's library, perhaps? Either way, if you just hit Cancel, it will disappear, you won't be able to play that particular song or use whatever type of content it was, but there's nothing to worry about under any circumstances. Perfectly normal behavior.
jW