It says sign into your Google account. I used Google in years past to search, but nothing else. So how do I have a Google account if I have no memory of ever having an account?
There are some sites which require either Yahoo, Disqus and or Google (blogger, Youtube) names to enter each sites forums if you want to make a post or comment.
The best example is if you have a Youtube account, then automatically...you have a Google account.