The only thing it shows is that decentralized structures are more stable than the centralized ones. Of course, Bitcoin is more stable because it's distributed all over the world, whereas Facebook is very centralized. That being said, it's an unfair comparison due to the nature of the outage and due to the functionality of these two. Facebook allegedly was down due to a buggy update, basically, that resulted in the Internet failing to find the addresses. Critical bugs also happened to Bitcoin before, and they were potentially devastating. So decentralized structures are better, but not invincible. As for functionality, Bitcoin has way fewer users and use cases. Tons of communication happens on Facebook, many activities are coordinated on this platform, whereas Bitcoin can only allow you to send coins, so not much.