Coinedup accesses and logs users in, via Google's unique OpenID designated to each Google account. So basically, if the PC through which you're logging in, is connected with a Google account other than yours, you will be logged in to that account instead of yours. It's not a security issue, simply because user of that computer NEVER logged out of his Google account on that computer and left logged in and that's why you were logged in directly to this account.