How does my just-booted and encrypted iPhone still receive messages before I decrypt it with the passcode?

It's my understanding that personal data on the iPhone 6 is automatically encrypted with the user's passcode. This is why when you boot it for the first time the passcode is required instead of the fingerprint.

My question, however, is why after the first boot, before entering the passcode for the first time, does the iPhone continue to receive account-specific notifications? As an example, Google Hangouts will actively receives messages that are readable and on the lock screen before any decryption has taken place. Wouldn't this imply that the user data for apps somehow are not encrypted?