Facebook want to increase its functionality in search engine, for that it is exposing all the public posts of users to google. Facebook recently indexed 2 trillion public posts. Now we can see posts, conversations, likes, pictures by inserting any phrases in search engine.
So on that point your public posts are available for universal search. Worlds biggest social network make it more easy by exposing posts. It just works like as Twitter and google search only. So beware that you are exposed to the world now by your posts. Lets just change settings of our profiles if we don’t want to reveal.
Step 2 : Limit the visibility of past posts