If you want to encrypt your data before you upload it, surely you have that option? In fact that really the only way it could work, if they did the encryption and have your back the key, you'd have to trust them that they're not keeping it too.
I can understand why they don't want to add a big barrier to entry by requiring that.
What I want to know if this uses any form of zero-knowledge cryptography features or not.
I guess not - since it can pull data directly from FB.