i do not recall making public the list of people with whom i have merely corresponded via gmail, isn't my inbox private?
The "friends of friends" bit is the one that could be creepy potentially, but here as well, all they do is take your friends emails, find other social services on the internet associated with those emails, and display the names of your "friends" (totally public) lists of friends.
This is something you could easily do manually with any search engine.