Originally Facebook was completely cut off from Google. All posts by personal profiles were hidden from the search engine, and you couldn’t do searches inside of Facebook that way. It appears that somehow Google has been able to get access, and some searches for Facebook content will display results with direct links to posts from personal profiles. This may have come from people sharing the links through other crawlable sites (such as Twitter). At any rate, some of these posts are now showing up in the Google SERPs.
Read the full article here:
Google Search Results Show Some Facebook User Posts Leaking Out Of Walled Garden